# Descriptive analysis and prognostic factors in cats with myeloma-related disorders: A multicenter retrospective study of 50 cases

Lorris Lecot, Isabelle Desmas-Bazelle, Sarah Benjamin, Pauline de Fornel, Frédérique Ponce, Matthew Kornya, Loic Desquilbet, Claire Beaudu-Lange, Catherine Ibisch, David Sayag, et al.

<figure><img src="image_1.png" /></figure>

## To cite this version:

Lorris Lecot, Isabelle Desmas-Bazelle, Sarah Benjamin, Pauline de Fornel, Frédérique Ponce, et al. Descriptive analysis and prognostic factors in cats with myeloma-related disorders: A multicenter retrospective study of 50 cases. Journal of Veterinary Internal Medicine, 2024, 38 (3), pp.1693-1705. 10.1111/jvim.17051. hal-04653983

HAL Id: hal-04653983

https://hal.inrae.fr/hal-04653983v1

Submitted on 19 Jul 2024

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# Descriptive analysis and prognostic factors in cats with myeloma-related disorders: A multicenter retrospective study of 50 cases

Lorris Lecot<fnref n="1" />,<fnref n="2" />

Isabelle Desmas-Bazelle<fnref n="3" />

Sarah Benjamin<fnref n="4" /> ID

<figure><img src="image_3.png" /></figure>

Pauline De Fornel<fnref n="5" />

Frédérique Ponce<fnref n="6" />

Matthew Kornya<fnref n="7" /> ID

<figure><img src="image_4.png" /></figure>

Loïc Desquilbet<fnref n="8" />

Claire Beaudu-Lange<fnref n="9" />

Catherine Ibisch<fnref n="10" />

David Sayag<fnref n="11" />

<figure><img src="image_5.png" /></figure>

Ghita Benchekroun<fnref n="1" />,<fnref n="12" /> ID

Jérémy Béguin<fnref n="1" />,<fnref n="13" /> ID

<figure><img src="image_6.png" /></figure>

**Correspondence**

Jérémy Béguin, Ecole Nationale Vétérinaire d'Alfort-CHUVA, Service de Médecine Interne, 7 Avenue du Général de Gaulle, F-94700 Maisons-Alfort, France.

Email: jeremy.beguin@vet-alfort.fr

**Abstract**

**Background:** Myeloma-related disorders (MRDs) are rare and poorly documented neoplasms of cats.

**Hypothesis/Objectives:** To describe clinical, clinicopathologic, and imaging findings, response to treatment, and survival time and to identify factors associated with shorter outcomes in cats with MRD.

**Animals:** Fifty cats with a diagnosis of MRD.

**Methods:** Cats with paraproteinemia confirmed by serum protein electrophoresis (SPE) and either intramedullary plasmacytosis >10%, marked cytonuclear atypia with intramedullary plasmacytosis that ranged between 5% and 10%, or cytologically or

**Abbreviations:** AEs, adverse events; AGR, albumin-to-globulin ratio; BM, bone marrow; CI, confidence interval; CKD, chronic kidney disease; COP, cyclophosphamide, vincristine and prednisolone; CR, complete remission; CT, computed tomography; EMP, extramedullary plasmacytoma; HR, hazard ratio; HVS, hyperviscosity syndrome; LCOP, L-asparaginase, cyclophosphamide, vincristine and prednisolone; MM, multiple myeloma; MRD, myeloma-related disorders; MST, median survival time; NLR, neutrophil-to-lymphocyte ratio; PD, progressive disease; PLR, platelet-to-lymphocyte ratio; RI, reference interval; RR, response rate; SPE, serum protein electrophoresis.

This is an open access article under the terms of the [Creative Commons Attribution License](https://creativecommons.org/licenses/by/4.0/), which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

© 2024 The Authors. *Journal of Veterinary Internal Medicine* published by Wiley Periodicals LLC on behalf of American College of Veterinary Internal Medicine.

<footnote n="1">¹Ecole Nationale Vétérinaire d'Alfort-CHUVA, Service de Médecine Interne, Maisons-Alfort, France</footnote>

<footnote n="2">²Université de Lyon, VetAgro Sup, Service de médecine interne, Marcy l'Etoile, France</footnote>

<footnote n="3">³Royal Veterinary College, London, UK</footnote>

<footnote n="4">⁴Davies Veterinary Specialists, Hitchin, UK</footnote>

<footnote n="5">⁵Micen Vet, Créteil, France</footnote>

<footnote n="6">⁶Université de Lyon, VetAgro Sup, Service de cancérologie, UR ICE, Marcy l'Etoile, France</footnote>

<footnote n="7">⁷Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada</footnote>

<footnote n="8">⁸Ecole nationale vétérinaire d'Alfort, IMRB, Maisons-Alfort, France</footnote>

<footnote n="9">⁹Clinique Vétérinaire de la Pierre bleue, Pipriac, France</footnote>

<footnote n="10">¹⁰Nantes-Atlantic College of Veterinary Medicine and Food Sciences (Oniris), Nantes, France</footnote>

<footnote n="11">¹¹Onconseil, Toulouse, France</footnote>

<footnote n="12">¹²Ecole Nationale Vétérinaire d'Alfort, Université Paris Est Créteil, INSERM, IMRB, Maisons-Alfort, France</footnote>

<footnote n="13">¹³UMR1161 VIROLOGIE, INRAE, Ecole Nationale Vétérinaire d'Alfort, ANSES, Université Paris-Est, Maisons-Alfort, France</footnote>
histologically confirmed visceral infiltration were retrospectively included from
several veterinary referral centers.

**Results:** Bone marrow plasmacytosis and splenic or hepatic involvement were present in 17/27 cats (63%), 36/42 cats (86%), and 27/38 cats (71%), respectively. Anemia was reported in 33/49 cats (67%) and thrombocytopenia in 16/47 cats (34%). Some of the treatments that the cats received included melphalan and prednisolone (n = 19), cyclophosphamide and prednisolone (n = 10), chlorambucil and prednisolone (n = 4), prednisolone (n = 4), or other (n = 4). The overall response rates to melphalan, cyclophosphamide, and chlorambucil in combination with prednisolone were 87%, 90%, and 100%, respectively. Adverse events to melphalan or cyclophosphamide occurred in 65% and 23% of cats, respectively. Median survival time was 122 days (range, 0-1403) and was not significantly associated with chemotherapy protocol. Anemia (hazard ratio [HR], 3.1; 95% confidence interval [CI], 1.0-9.8) and thrombocytopenia (HR, 2.7; 95% CI, 1.2-6.0) were risk factors for shorter survival.

**Conclusions and Clinical Importance:** Our study confirmed the guarded prognosis of MRD in cats and identified risk factors for shorter survival times.

KEYWORDS

cat, oncology, plasma cell, prognosis

# 1 | INTRODUCTION

Myeloma-related disorders (MRD) represent <1% of all malignancies and 1.9% of hematologic malignancies in cats.¹,² In dogs, the diagnostic criteria of multiple myeloma (MM) include the presence of >20% neoplastic plasma cells in the bone marrow (BM) and at least one the following criteria: serum paraproteinemia, immunoglobulin light chain (Bence Jones) proteinuria, and osteolytic lesions.³⁻⁵ Historically, the previous diagnostic criteria have been applied to cats.⁶⁻⁸ However, abdominal organ involvement without substantial BM infiltration appears more frequently in cats than in dogs.⁹⁻¹¹ Indeed, splenic (83%-100%) or hepatic (89%-100%) infiltration and atypical plasma cell morphology (67%-93.3%) without substantial BM infiltration were commonly reported in cats with MRD.⁹⁻¹¹ The distinction between MM and multicentric noncutaneous extramedullary plasmacytoma (EMP) within the MRD is unclear because of the occurrence of systemic involvement in cats. Multiple myeloma (cases with BM plasmacytosis) and multicentric noncutaneous EMP (spleen or liver plasmacytosis or both without BM involvement) will be referred to as MRD in our study. Current recommendations require 2 of the following criteria for the diagnosis of MRD in cats: (1) >10% BM plasmacytosis or >5% atypical plasma cells; (2) paraproteinemia; (3) osteolytic lesions; (4) light chain proteinuria; and, (5) visceral organ involvement.¹,¹⁰

Only 4 studies on MRD in cats assessing treatment response with an alkylating agent in combination with prednisolone have been published.⁸⁻¹⁰,¹² One study reported a 71% response rate (RR) to melphalan and prednisolone.¹² However, this protocol was associated with myelosuppression leading to treatment discontinuation.¹² Good

tolerance and a RR of 83% were reported with cyclophosphamide and prednisolone, which currently is considered the first-line treatment for MRD in cats.¹²

Median survival time (MST) of cats diagnosed with MRD appears to be worse than for dogs, ranging between 5 days and 12.3 months.⁸⁻¹⁰,¹² Although prognostic factors have been identified in dogs, no prognostic factors have been established in cats.¹³⁻³⁵ Classification into 2 categories (aggressive vs nonaggressive) based on several negative prognostic criteria (hypercalcemia, osteolytic lesions with pathological fractures, anemia, Bence Jones proteinuria, azotemia, persistently high serum protein concentration after 8 weeks of treatment and little or no clinical improvement) has been proposed for cats.⁸ Median survival time of 5 days for the aggressive category and 387 days for the less aggressive category were reported, but no rigorous statistical analysis was performed.⁸

Our primary objective was to describe the epidemiological and clinicopathological findings of systemic MRD in cats. The second objective was to describe outcomes and tolerance to treatment. The third objective was to identify factors associated with shorter survival times (ST).

# 2 | MATERIALS AND METHODS

## 2.1 | Case selection

The medical records of cats diagnosed with MRD from January 2005 to June 2022 at 14 referral centers were retrospectively reviewed
(Royal Veterinary College, National Veterinary School of Alfort, Davies Veterinary Specialists, Micenvet, Ontario Veterinary College, VetAgro Sup, the Royal (Dick) School of Veterinary Studies, Onconseil, Oniris, Advetia, AURA veterinary, CENTREDMVET DMV, Liverpool University, Veterinary clinic of la Pierre Bleue).

## 2.2 | Diagnostic criteria of MRD

Cats were retrospectively included based on the presence of hyperglobulinemia attributable to paraproteinemia as evidenced by serum protein electrophoresis (SPE) and 1 of the following criteria: BM plasmacytosis >10% or marked cytonuclear atypia if the BM plasmacytosis ranged between 5% and 10% or visceral plasma cell infiltration confirmed by cytological or histological examination. Medical records were reviewed by a single author (LL). No minimal duration of follow-up was required.

## 2.3 | Data collection

The following data were obtained from the medical records: breed, age, sex, weight, spay or neuter status, comorbidities and concomitant medications, clinical signs, and physical examination findings. The results of CBC and blood smear examination, biochemical analysis, serum (SPE) and urine protein electrophoresis and immunoglobulin type as determined by radial immunodiffusion, urinalysis, noninvasive blood pressure, fundic examination, thoracic and abdominal radiographs or ultrasound examinations, computed tomography (CT) scans, BM aspiration, cytological or histological analyses, and immunohistochemistry analyses were recorded. Regarding treatment, drug, dosage, frequency of administration, time to response (partial or complete), rescue treatment protocols and adverse events (AEs) were recorded. Adverse events associated with chemotherapy were graded according to the Veterinary Cooperative Oncology Group criteria for AEs.³⁶ Regarding outcome, remission status, duration of remission, date of relapse (defined as occurrence of progressive disease [PD] after complete remission [CR] or partial response [PR]), date of last follow-up if lost to follow-up, date and cause of death and necropsy results if performed were recorded. Complete remission was defined as the resolution of hyperglobulinemia. Partial response was defined as at least a 30% decrease in globulin or the total protein concentrations without complete resolution, PD as at least a 20% increase in globulin or the total protein concentrations, and stable disease (SD) as an insufficient change to qualify for either PR or PD.¹² Partial response, PD, and SD were defined based on total protein concentrations because serum globulin concentration was not measured at each assessment.¹² The time to response was determined as the duration from the initiation of treatment to the occurrence of the first documented CR or PR. Follow-up assessments were conducted every 10 to 15 days in the first month and subsequently at least once a month until CR, PD, or chemotherapy-related toxicity

was noticed. For patients achieving CR, reevaluation were performed every 2 months.

## 2.4 | Statistical analysis

All statistical analyses were performed using commercially available software (SAS University Edition) under the supervision of an epidemiologist (LD). Continuous variables are presented as medians (range). Qualitative variables are presented as a percentage corresponding to the number of cats affected out of the number of cats for which the information was available. To identify factors associated with overall survival time (OST) and to compare outcomes between initial chemotherapy treatments (cyclophosphamide vs melphalan), survival analysis was performed by using Kaplan-Meier curves and the log-rank test. Survival time was defined as the time between diagnosis and either the date of all-cause death or the date of censoring. Censored individuals were those either still alive at the end of the study (June 01, 2023) or those lost to follow-up. Individuals were censored at the time of the last follow-up available. The following exposures were used as dichotomous variables: anemia (PCV < 30%), azotemia (serum creatinine concentration > 1.58 mg/dL [140 µmol/L]), total (tCa) and ionized (iCa) hypercalcemia (tCa > 2.8 mmol/L or iCa > 1.4 mmol/L), osteolytic lesions, splenic or hepatic involvement or both (cytologically or histologically confirmed), increased liver enzyme activity (alkaline phosphatase or alanine aminotransferase), hyperbilirubinemia, hypoalbuminemia, marked hyperglobulinemia (defined below), low albumin-to-globulin ratio (AGR; defined below), proteinuria (urine protein-to-creatinine ratio > 0.4), Bence Jones proteinuria on urine protein electrophoresis, BM infiltration, BM cell atypia, rouleaux formation, monoclonal vs biclonal hypergammaglobulinemia on SPE, leukopenia, neutropenia, lymphopenia, thrombocytopenia, circulating plasma cells, high neutrophil-to-lymphocyte ratio (NLR; defined below), high platelet-to-lymphocyte ratio (PLR); (defined below), hyperviscosity syndrome (HVS), systemic arterial hypertension, pleural or abdominal effusion, positive FIV or FelV SNAP test (IDEXX Labs). As reference interval (RI) was similar among institutions for anemia, azotemia, hypercalcemia and proteinuria, clear cutoffs were selected for these variables. Increased liver enzyme activity, hyperbilirubinemia, hypoalbuminemia, leukopenia, neutropenia, lymphopenia and thrombocytopenia were defined as results outside of the individual laboratory RIs. Hyperviscosity syndrome was defined by the presence of at least 1 of the following: bleeding diathesis (epistaxis, petechiae, ecchymosis, gingival bleeding), central nervous system signs (seizures, stupor, coma), or fundus examination abnormality (dilated or tortuous retinal vessels, retinal hemorrhage, retinal detachment). No established cutoffs for AGR, NLR, PLR and hyperglobulinemia are available for cats diagnosed with MRD. Therefore, these variables were recoded into binary variables according to the first or the second tertile. A low AGR was defined as a value below the first tertile of the cohort. High NLR, high PLR, and marked hyperglobulinemia were defined as results
above the second tertile of the cohort. Survival analysis was performed based on the aggressive vs nonaggressive classification.⁸

Crude and adjusted hazard ratios along with their 95% confidence intervals were calculated using Cox proportional hazards analysis. The variables included in the multivariate model as potential confounders were variables that were significant at *P* < .20 in the univariate analysis. Statistical significance was set at *P* < .05.

## 3 | RESULTS

### 3.1 | Patient signalment

Fifty cats (43 domestic shorthair cats, 22 Bengal cats, 2 Maine coon cats, 1 Norwegian cat, and 1 Chartreux cat) were included. Thirty-two cats (64%) were castrated males, and 18 cats (36%) were spayed females. The median age was 12.0 years (range, 4.0-17.5 years). The median body weight was 4.85 kg (range, 2.64-9.90 kg).

### 3.2 | Clinical and paraclinical findings

Presenting complaints, clinical signs, and paraclinical findings are summarized in Tables 1 and 2.

The most frequent presenting complaints were lethargy (68%), anorexia (64%), and weight loss (62%). At the time of diagnosis, all cats were hyperglobulinemic (median, 98 g/L; range, 50-170 g/L). Biclonal gammopathy was recorded in 2/44 cats (5%). Thirty-six of 42 cats (86%) had splenic involvement, and 27/38 (71%) had liver involvement. Twenty-three of 37 cats (62%) had both splenic and hepatic involvement. Seventeen of 27 cats (63%) had BM plasmacytosis. Among them, 11/17 cats had BM plasmacytosis >10%, and 6/17 had BM plasmacytosis ranging between 5% and 10% with marked cytonuclear atypia. Ten of 23 cats (43%) had spleen or liver involvement without BM plasmacytosis. Two of 23 cats (9%) had BM plasmacytosis without spleen or liver involvement. Two of 47 cats had circulating plasma cells. Among these cats, 1 had BM plasmacytosis along with spleen and liver involvement and the other had spleen and liver involvement without BM plasmacytosis.

### 3.3 | Diagnostic imaging

Imaging findings are summarized in Table 3.

Abdominal ultrasonography was performed at the time of diagnosis in 42 cats. For 3 cats, cytologic examinations of the liver and spleen were not consistent with visceral infiltration. Among these 3 cats, hepatomegaly was reported in 1 cat, whereas abdominal ultrasonography was within normal limits in the others.

In 2 cats, a bone biopsy was performed, and plasma cell infiltration of osteolytic lesions was confirmed. Pathological fractures were identified in 2 cats.

<table><caption>TABLE 1 Presenting complaints, clinical signs and comorbidities of cats diagnosed with MRD.</caption><thead><tr><th>Observation</th><th>Number of cats affected/ number of cats tested</th><th>Percentage of cats affected</th></tr></thead><tbody><tr><td>Lethargy</td><td>34/50</td><td>68%</td></tr><tr><td>Anorexia</td><td>32/50</td><td>64%</td></tr><tr><td>Weight loss</td><td>31/50</td><td>62%</td></tr><tr><td>Pale mucous membrane</td><td>15/50</td><td>30%</td></tr><tr><td>Polyuria/polydipsia</td><td>14/50</td><td>28%</td></tr><tr><td>Dehydration</td><td>14/50</td><td>28%</td></tr><tr><td>Cardiac arrhythmia/murmur</td><td>14/50</td><td>28%</td></tr><tr><td>Abdominal organomegaly</td><td>12/50</td><td>24%</td></tr><tr><td>Vomiting</td><td>11/50</td><td>22%</td></tr><tr><td>Ocular abnormalities<sup>a</sup></td><td>5/26</td><td>19%</td></tr><tr><td>Periodontal disease</td><td>8/50</td><td>16%</td></tr><tr><td>Fever</td><td>7/50</td><td>14%</td></tr><tr><td>Recurrent respiratory infection</td><td>7/50</td><td>14%</td></tr><tr><td>Lameness</td><td>4/50</td><td>8%</td></tr><tr><td>Neurologic signs<sup>b</sup></td><td>4/50</td><td>8%</td></tr><tr><td>Diarrhea</td><td>3/50</td><td>6%</td></tr><tr><td>Bleeding disorders</td><td>3/50</td><td>6%</td></tr><tr><td>Peripheral lymphadenopathy</td><td>3/50</td><td>6%</td></tr><tr><td>Cutaneous lesions</td><td>1/50</td><td>2%</td></tr><tr><td>Comorbidities</td><td></td><td></td></tr><tr><td>Chronic kidney disease (treatment = renal diet)</td><td>2/50</td><td>4%</td></tr><tr><td>Hyperthyroidism (treatment = thiamazole)</td><td>2/50</td><td>4%</td></tr><tr><td>Feline lower urinary tract disease (treatment = urinary diet)</td><td>1/50</td><td>2%</td></tr><tr><td>Feline inflammatory bronchial disease (treatment = systemic prednisolone)</td><td>1/50</td><td>2%</td></tr><tr><td>Toxoplasmosis (treatment = clindamycin)</td><td>1/50</td><td>2%</td></tr><tr><td>Mycoplasmosis (treatment = doxycycline)</td><td>1/50</td><td>2%</td></tr></tbody></table>

### 3.4 | Treatment

Four cats were lost to follow-up before treatment initiation. Treatment was initiated in 41/46 cats (89%). Nineteen cats (46%) received melphalan (0.1 mg/kg/day PO for 10 days and 0.05 mg/kg/day PO thereafter) and corticosteroids (prednisolone or dexamethasone) as initial chemotherapy. Ten cats (24%) were treated with cyclophosphamide (200 mg/m² PO every 2-3 weeks) and

<footnote><sup>a</sup>Ocular abnormalities such as mydriasis, tortuous retinal vessels, retinal hemorrhage, retinal detachment or chorioretinitis.</footnote>

<footnote><sup>b</sup>Neurologic signs include abnormal mentation, seizure activity or cranial nerve deficits corresponding to thalamocortical or brainstem lesion.</footnote>
<table><caption>TABLE 2 Paraclinical abnormalities of cats diagnosed with MRD.</caption><thead><tr><th>Observation</th><th>Number of cats affected/number of cats tested</th><th>Percentage of cats affected</th><th>Median</th><th>Range</th></tr></thead><tbody><tr><td>Diagnostic criteria</td><td></td><td></td><td></td><td></td></tr><tr><td>Hyperglobulinemia<sup>a</sup></td><td>50/50</td><td>100%</td><td>98 g/L</td><td>50-170 g/L</td></tr><tr><td>Hypergammaglobulinemia</td><td>44/44</td><td>100%</td><td></td><td></td></tr><tr><td>Monoclonal</td><td>42/44</td><td>95%</td><td></td><td></td></tr><tr><td>Biclonal</td><td>2/44</td><td>5%</td><td></td><td></td></tr><tr><td>Bence Jones proteinuria</td><td>8/17</td><td>47%</td><td></td><td></td></tr><tr><td>Bone marrow plasmacytosis</td><td>17/27</td><td>63%</td><td></td><td></td></tr><tr><td>&gt;10%</td><td>11/27</td><td>41%</td><td>30%</td><td>5%-80%</td></tr><tr><td>&lt;10%</td><td>6/27</td><td>22%</td><td></td><td></td></tr><tr><td>Abdominal organ involvement<sup>b</sup></td><td></td><td></td><td></td><td></td></tr><tr><td>Spleen</td><td>36/42</td><td>86%</td><td></td><td></td></tr><tr><td>Liver</td><td>27/38</td><td>71%</td><td></td><td></td></tr><tr><td>Spleen and liver</td><td>23/37</td><td>62%</td><td></td><td></td></tr><tr><td>Other</td><td>3/48 (kidney: 2 unilateral, 1 bilateral)</td><td>6%</td><td></td><td></td></tr><tr><td></td><td>1/48 (splenic and colic lymph nodes)</td><td>2%</td><td></td><td></td></tr><tr><td></td><td>1/48 (lung)</td><td>2%</td><td></td><td></td></tr><tr><td>Thoracic organ involvement<sup>b</sup></td><td>1/48 (mediastinal lymph node)</td><td>2%</td><td></td><td></td></tr><tr><td>Osteolytic lesions<sup>c</sup></td><td>11/38</td><td>29%</td><td></td><td></td></tr><tr><td>Other paraclinical abnormalities</td><td></td><td></td><td></td><td></td></tr><tr><td>Hypoalbuminemia<sup>d</sup></td><td>29/49</td><td>59%</td><td>23 g/L</td><td>14-37 g/L</td></tr><tr><td>Ionized hypercalcemia (iCa &gt; 1.4 mmol/L)</td><td>6/36</td><td>17%</td><td>1.21 mmol/L</td><td>1.1-1.65 mmol/L</td></tr><tr><td>Azotemia (creatinine &gt;140 µmol/L)</td><td>20/48</td><td>42%</td><td>175 µmol/L</td><td>17-1733 µmol/L</td></tr><tr><td>Increased liver enzyme activity<sup>a</sup></td><td>16/40</td><td>40%</td><td>ALT: 61 U/L<br>ALP: 32 U/L</td><td>ALT: 0-1673 U/L<br>ALP: 6-586 U/L</td></tr><tr><td>Hyperbilirubinemia<sup>a</sup></td><td>5/27</td><td>19%</td><td>0.3 mg/dL</td><td>0-19.6 mg/dL</td></tr><tr><td>Bone marrow plasma cell atypia</td><td>15/25</td><td>60%</td><td></td><td></td></tr><tr><td>Anemia (PCV &lt; 30%)</td><td>33/49</td><td>67%</td><td>22.1%</td><td>9.0%-46.0%</td></tr><tr><td>Rouleaux formation</td><td>29/42</td><td>69%</td><td></td><td></td></tr><tr><td>Leucopenia<sup>d</sup></td><td>12/49</td><td>24%</td><td>6.2 × 10<sup>9</sup>/L</td><td>0.8-26.0 × 10<sup>9</sup>/L</td></tr><tr><td>Neutropenia<sup>d</sup></td><td>10/47</td><td>21%</td><td>4.7 × 10<sup>9</sup>/L</td><td>0.5-24.5 × 10<sup>9</sup>/L</td></tr><tr><td>Lymphopenia<sup>d</sup></td><td>27/47</td><td>57%</td><td>0.8 × 10<sup>9</sup>/L</td><td>0.1-2.6 × 10<sup>9</sup>/L</td></tr><tr><td>Thrombocytopenia<sup>d</sup></td><td>16/47</td><td>34%</td><td>156.5 × 10<sup>9</sup>/L</td><td>22.0-650.0 × 10<sup>9</sup>/L</td></tr><tr><td>Circulating plasma cells</td><td>2/47</td><td>4%</td><td></td><td></td></tr><tr><td>Hyperviscosity syndrome</td><td>9/27</td><td>33%</td><td></td><td></td></tr><tr><td>Systemic arterial hypertension</td><td>3/17</td><td>18%</td><td>140 mmHg</td><td>84-210 mmHg</td></tr><tr><td>Proteinuria (UPC &gt; 0.4)</td><td>13/23</td><td>57%</td><td>1.0</td><td>0.3-9.5</td></tr><tr><td>Pleural or abdominal effusion</td><td>12/49 (1 cat confirmed with bilateral myelomatous pleural effusion)</td><td>24%</td><td></td><td></td></tr><tr><td>FIV/FeLV status<sup>e</sup></td><td>1/8 (positive for FeLV antigen)</td><td>13%</td><td></td><td></td></tr></tbody></table>

<footnote><sup>a</sup>Above reference interval.</footnote>

<footnote><sup>b</sup>Visceral involvement based on ante-mortem cytological or histological analyses.</footnote>

<footnote><sup>c</sup>Osteolytic lesions based on CT scan or radiographic examinations.</footnote>

<footnote><sup>d</sup>Below reference interval and confirmed by blood smear examination.</footnote>

<footnote><sup>e</sup>SNAP test (IDEXX Labs).</footnote>
<table><caption>TABLE 3 Imaging findings of cats diagnosed with MRD.</caption><thead><tr><th>Observation</th><th>Number of cats affected/ number of cats tested</th><th>Percentage of cats affected</th></tr></thead><tbody><tr><td>Abdominal ultrasonography (n = 42)</td><td></td><td></td></tr><tr><td>Splenic ultrasonographic abnormalities in cats with cytologic or histopathologic confirmed splenic involvement</td><td>22/36</td><td>61%</td></tr><tr><td>Splenomegaly</td><td>17/22</td><td>77%</td></tr><tr><td>Hyperechoic nodules</td><td>9/22</td><td>41%</td></tr><tr><td>Mottled appearance</td><td>8/22</td><td>36%</td></tr><tr><td>Hypoechoic nodules</td><td>4/22</td><td>18%</td></tr><tr><td>Hypoechoic parenchyma</td><td>4/22</td><td>18%</td></tr><tr><td>Hepatic ultrasonographic abnormalities in cats with cytologic or histopathologic confirmed hepatic involvement</td><td>24/27</td><td>89%</td></tr><tr><td>Hepatomegaly</td><td>13/24</td><td>54%</td></tr><tr><td>Hyperechoic parenchyma</td><td>7/24</td><td>29%</td></tr><tr><td>Hyperechoic nodules</td><td>5/24</td><td>21%</td></tr><tr><td>Mottled appearance</td><td>4/24</td><td>17%</td></tr><tr><td>Hypoechoic parenchyma</td><td>3/24</td><td>13%</td></tr><tr><td>Hypoechoic nodules</td><td>3/24</td><td>13%</td></tr><tr><td>Thoracic radiographs (n = 26)</td><td></td><td></td></tr><tr><td>Normal</td><td>14/26</td><td>54%</td></tr><tr><td>Interstitial pulmonary pattern</td><td>5/26</td><td>19%</td></tr><tr><td>Pleural effusion</td><td>4/26</td><td>15%</td></tr><tr><td>Vertebral or costal osteolytic lesions</td><td>3/26</td><td>12%</td></tr><tr><td>Mediastinal lymphadenopathy</td><td>3/26</td><td>12%</td></tr><tr><td>Enlarged cardiac silhouette</td><td>3/26</td><td>12%</td></tr><tr><td>Lung nodule</td><td>1/26</td><td>4%</td></tr><tr><td>Localization of osteolytic lesions assessed by complete survey radiographs (n = 30) or whole body computed tomography (n = 8)</td><td></td><td></td></tr><tr><td>Vertebral bodies</td><td>9/38</td><td>24%</td></tr><tr><td>Pelvis</td><td>4/38</td><td>11%</td></tr><tr><td>Spinous processes</td><td>3/38</td><td>8%</td></tr><tr><td>Ribs</td><td>2/38</td><td>5%</td></tr><tr><td>Humerus</td><td>2/38</td><td>5%</td></tr><tr><td>Femur</td><td>2/38</td><td>5%</td></tr><tr><td>Radius</td><td>1/38</td><td>3%</td></tr><tr><td>Ulna</td><td>1/38</td><td>3%</td></tr><tr><td>Scapula</td><td>1/38</td><td>3%</td></tr><tr><td>Phalanges</td><td>1/38</td><td>3%</td></tr><tr><td>Pathological fracture assessed by complete survey radiographs (n = 30) or whole body computed tomography (n = 8)</td><td>2/38</td><td>5%</td></tr></tbody></table>

<table><caption>TABLE 4 Chemotherapy-related adverse events in cats with MRD treated with prednisolone and melphalan, cyclophosphamide or chlorambucil.</caption><thead><tr><th>Adverse events</th><th>Melphalan and prednisolone (n = 20)</th><th>Cyclophosphamide and prednisolone (n = 13)</th><th>Chlorambucil and prednisolone (n = 5)</th></tr></thead><tbody><tr><td><strong>Neutropenia</strong></td><td><strong>11 (55%)</strong></td><td><strong>2 (15%)</strong></td><td><strong>0 (0%)</strong></td></tr><tr><td>Grade 1</td><td>3 (15%)</td><td>0 (0%)</td><td>0 (0%)</td></tr><tr><td>Grade 2</td><td>2 (10%)</td><td>2 (15%)</td><td>0 (0%)</td></tr><tr><td>Grade 3</td><td>3 (15%)</td><td>0 (0%)</td><td>0 (0%)</td></tr><tr><td>Grade 4</td><td>3 (15%)</td><td>0 (0%)</td><td>0 (0%)</td></tr><tr><td>Grade 5</td><td>0 (0%)</td><td>0 (0%)</td><td>0 (0%)</td></tr><tr><td><strong>Anemia</strong></td><td><strong>3 (15%)</strong></td><td><strong>1 (8%)</strong></td><td><strong>0 (0%)</strong></td></tr><tr><td>Grade 1</td><td>0 (0%)</td><td>0 (0%)</td><td>0 (0%)</td></tr><tr><td>Grade 2</td><td>1 (5%)</td><td>0 (0%)</td><td>0 (0%)</td></tr><tr><td>Grade 3</td><td>2 (10%)</td><td>1 (8%)</td><td>0 (0%)</td></tr><tr><td>Grade 4</td><td>0 (0%)</td><td>0 (0%)</td><td>0 (0%)</td></tr><tr><td>Grade 5</td><td>0 (0%)</td><td>0 (0%)</td><td>0 (0%)</td></tr><tr><td><strong>Thrombocytopenia</strong></td><td><strong>2 (10%)</strong></td><td><strong>0 (0%)</strong></td><td><strong>0 (0%)</strong></td></tr><tr><td>Grade 1</td><td>0 (0%)</td><td>0 (0%)</td><td>0 (0%)</td></tr><tr><td>Grade 2</td><td>1 (5%)</td><td>0 (0%)</td><td>0 (0%)</td></tr><tr><td>Grade 3</td><td>1 (5%)</td><td>0 (0%)</td><td>0 (0%)</td></tr><tr><td>Grade 4</td><td>0 (0%)</td><td>0 (0%)</td><td>0 (0%)</td></tr><tr><td>Grade 5</td><td>0 (0%)</td><td>0 (0%)</td><td>0 (0%)</td></tr><tr><td><strong>Gastrointestinal signs</strong></td><td><strong>2 (10%)</strong></td><td><strong>1 (8%)</strong></td><td><strong>0 (0%)</strong></td></tr><tr><td>Vomiting: grade 1</td><td>0 (0%)</td><td>1 (8%)</td><td>0 (0%)</td></tr><tr><td>Diarrhea: grade 2</td><td>1 (5%)</td><td>0 (0%)</td><td>0 (0%)</td></tr><tr><td>Nausea: grade 2</td><td>1 (5%)</td><td>0 (0%)</td><td>0 (0%)</td></tr></tbody></table>

Note: Grading according to VCOG criteria.³⁶ Data are presented as number (%).

corticosteroids as first-line treatment. Four cats (10%) received chlorambucil (2 mg per cat PO every other day) and corticosteroids as initial chemotherapy. Four cats (10%) were treated with corticosteroids alone as first-line treatment. Four cats (10%) received other treatments, including dexamethasone and vincristine (n = 1), L-asparaginase, cyclophosphamide, vincristine, and prednisolone (LCOP) protocol (n = 1), L-asparaginase with corticosteroids and chlorambucil (n = 1) and L-asparaginase with corticosteroids (n = 1) as initial chemotherapy. For all cats treated with prednisolone, the dosage ranged between 0.5 and 2 mg/kg/day.

Seven cats had several chemotherapy protocols either because of AEs or PD. Two cats had 4 protocols (chlorambucil/corticosteroid, followed by melphalan/corticosteroid, followed by cyclophosphamide/corticosteroid, followed by vincristine [n = 1]; cyclophosphamide/corticosteroid followed by melphalan/corticosteroid followed by lomustine, followed by cyclophosphamide/vincristine/prednisolone [COP] protocol [n = 1]). Two cats had 3 protocols (melphalan/corticosteroid, followed by cyclophosphamide/corticosteroid, followed by
vincristine/corticosteroid [n = 1]; cyclophosphamide/corticosteroid, followed by chlorambucil/corticosteroid, followed by melphalan/corticosteroid [n = 1]). Three cats had 2 protocols (cyclophosphamide/corticosteroid, followed by melphalan/corticosteroid [n = 1]; melphalan/corticosteroid, followed by cyclophosphamide/corticosteroid [n = 1]; cyclophosphamide/corticosteroid, followed by chlorambucil/corticosteroid [n = 1]). The interval of drug administration was increased for 3 cats treated with melphalan and 1 with cyclophosphamide.

Analgesics such as gabapentin (8-15 mg/kg PO q12h; n = 8), tramadol (2-3 mg/kg PO q12h; n = 2) and alendronate (10 mg per cat PO once weekly; n = 1) also were administered.

## 3.5 | Adverse events

Chemotherapy-related AEs from both initial and rescue chemotherapy protocols are summarized in Table 4.

Among the cats for which follow-up was available, AEs were reported in 13/20 cats (65%) treated with melphalan, 3/13 cats (23%) treated with cyclophosphamide and 0/5 cats treated with chlorambucil. No AEs were reported with other protocols.

## 3.6 | Response

Among the 16 cats treated with melphalan and corticosteroids with evaluable follow-up for response to treatment, 13 (81%)

achieved CR, and 1 achieved PR (6%). The overall RR was 87%. The median time to response was 47 days (range, 14-180 days). One cat achieved CR with melphalan after PD with chlorambucil. Among 10 cats treated with cyclophosphamide and corticosteroids with evaluable follow-up, 7 cats (70%) achieved CR, and 3 cats achieved PR (30%). The overall RR was 100%. The median time to response was 27 days (range, 5-161 days). One cat achieved CR with cyclophosphamide after PD with melphalan.

Among the 4 cats treated with chlorambucil and corticosteroids with evaluable follow-up, 1 cat (25%) achieved CR, and 3 cats achieved PR (75%). The overall RR was 100%. The time to remission was only known in 3 cats and was 12 (PR), 30 (PR), and 42 (CR) days. One cat maintained PR after replacement of cyclophosphamide with chlorambucil.

Among the 4 cats treated with corticosteroids alone, only 1 of 3 evaluable cats experienced PR after 50 days of treatment. The overall RR was 33%. For the cats treated with dexamethasone and vincristine (n = 1), the LCOP protocol (n = 1), L-asparaginase, chlorambucil and corticosteroids (n = 1) and L-asparaginase with corticosteroids (n = 1) as initial chemotherapy, there was no assessment regarding the response to treatment.

## 3.7 | Outcome

The outcomes of the treated cats are summarized in Figure 1.

<figure><img src="image_7.png" /><figcaption>FIGURE 1 Outcome of treated cats (n = 41). One bar represents 1 cat. The abscissa represents time, and the ordinate represents each case.</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>**FIGURE 2** Kaplan-Meier curve of OST for cats with anemia (n = 32; blue line) and cats without anemia (n = 13; red line). Cats with anemia had an OST of 89 days (range, 0-644 days), whereas cats without anemia had an OST of 356 days (range, 22-356 days; *P* = .01).</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>**FIGURE 3** Kaplan-Meier curve of OST for cats with thrombocytopenia (n = 15; blue line) and cats without thrombocytopenia (n = 28; red line). Cats with thrombocytopenia had an OST of 22 days (range, 0-311 days), whereas cats without thrombocytopenia had an OST of 156 days (range, 2-656 days; *P* < .01).</figcaption></figure>

Fifteen cats were lost to follow-up, and 6 were still alive at the end of the follow-up period (153, 240, 284, 365, 780, and 1403 days after diagnosis). Twenty-one cats were censored in the survival analysis. Of the remaining 29 cats, 27 cats were suspected to have died from MRD, 1 cat secondary to arterial thromboembolism, and 1 secondary to chronic kidney disease (CKD). The median follow-up period was 80 days (range, 0-1403 days).

## 3.8 | Survival analysis

The estimated overall MST was 122 days. The MST of the cats treated with melphalan or cyclophosphamide plus corticosteroids as initial treatment, with the exclusion of cats not treated or treated with other protocols, was 315 days.

Median survival time was not significantly different between the cats treated with melphalan (145 days) or cyclophosphamide plus corticosteroids (median not reached) as initial chemotherapy (*P* = .30).

<figure><img src="image_10.png" /><figcaption>**FIGURE 4** Kaplan-Meier curve of OST for cats with hypoalbuminemia (n = 27; blue line) and cats without hypoalbuminemia (n = 18; red line). Cats with hypoalbuminemia had an OST of 78 days (range, 0-667 days), whereas cats without hypoalbuminemia had an OST of 367 days (range, 2-589 days; *P* = .03).</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>**FIGURE 5** Kaplan-Meier curve of OST for cats with AGR ≤0.2 (n = 15; blue line) and cats with AGR > 0.2 (n = 29; red line). Cats with AGR ≤0.2 had an OST of 67 days (range, 2-667 days), whereas cats with AGR > 0.2 had an OST of 322 days (range, 0-589 days; *P* = .02).</figcaption></figure>

Results of CBCs were available for 40 cats for NLR analysis. The CBCs and blood smear examinations to evaluate platelet count were available for 38 cats for PLR analysis. Forty-nine and 48 cats were included in the marked hyperglobulinemia and AGR analysis, respectively. For 1 cat, the globulin concentration was reported to be >120 g/L, and for the other cat, the albumin concentration was not available, precluding quantitative analysis and AGR measurement.

The cutoffs for AGR, NLR, PLR, and marked hyperglobulinemia as predictors of OST were 0.2 (range, 0.11-0.64), 7.83 (range, 1.07-93.33), 260 (range, 9.21-844.16), and 110.7 g/L (range, 50.5-170 g/L), respectively. Based on those cutoffs, the cats were divided into the following groups: high AGR (AGR ≥ 0.2; n = 29), low NLR (NLR < 7.83; n = 28), low PLR (PLR < 260; n = 26), and marked hyperglobulinemia (globulins ≥ 110.7 g/L; n = 15).

In the univariate analysis, anemia (Figure 2), thrombocytopenia (Figure 3), hypoalbuminemia (Figure 4), and low AGR (Figure 5) at diagnosis were significantly associated with shorter ST. None of the other factors tested were significantly associated with shorter ST.
<table><caption>TABLE 5 Results from the multivariate Cox proportional hazards model for all-cause death in 50 cats with myeloma-related disorders.</caption><thead><tr><th rowspan="2">Variable</th><th rowspan="2">Hazard ratio</th><th colspan="3">95% CI for HR</th></tr><tr><th>Lower</th><th>Upper</th><th>P-value</th></tr></thead><tbody><tr><td>Anemia (vs no anemia)</td><td>3.14</td><td>1.00</td><td>9.82</td><td>.04</td></tr><tr><td>Thrombocytopenia (vs no thrombocytopenia)</td><td>2.68</td><td>1.19</td><td>6.05</td><td>.02</td></tr><tr><td>Hypoalbuminemia (vs no hypoalbuminemia)</td><td>1.91</td><td>0.78</td><td>4.69</td><td>.16</td></tr><tr><td>Low AGR (vs AGR ≥ 0.2)</td><td>0.96</td><td>0.34</td><td>2.74</td><td>.94</td></tr></tbody></table>

Abbreviations: CI, confidence intervals; HR, hazard ratio.

Variables with $P < 0.2$ in the univariate analysis (anemia, thrombocytopenia, hypoalbuminemia, and low AGR) were analyzed using Cox proportional hazards analysis. In the final multivariable model, anemia ($P = .04$) or thrombocytopenia ($P = .02$) at diagnosis were significantly associated with shorter ST (Table 5). Among cats with anemia, median hematocrit at diagnosis was 19.4% (range, 9%-26.6%). Among cats with thrombocytopenia, median platelet count at diagnosis was $94 \times 10^9/L$ (range, $22-138 \times 10^9/L$).

## 4 | DISCUSSION

We report similar epidemiological and clinicopathological findings as previous case series.⁶⁻¹¹ Our study confirmed that visceral involvement was more common than BM plasmacytosis. Moreover, we confirmed good tolerance and RR associated with cyclophosphamide administration. In this cohort, anemia and thrombocytopenia were associated with shorter survival times, independent of hypoalbuminemia and low AGR.

Visceral organ involvement without BM infiltration appears frequent in cats with MRD.⁹⁻¹¹ In cats with 10% to 20% BM plasmacytosis, diagnosis can be made on the assessment of plasma cell morphology in BM.¹,⁹⁻¹¹ Normal BM contains <5% plasma cells.¹ In our study, we included cases with BM plasmacytosis below 10% ($n = 6$) with cellular atypia and visceral organ involvement. Our study emphasizes visceral involvement and BM cellular atypia as main criteria for the diagnosis of MRD even if BM plasmacytosis is between 5% and 10%.¹,⁹⁻¹¹

Our study shares several variables with prior studies. Indeed, our results emphasize the nonspecific nature of the clinical signs (lethargy, anorexia and weight loss) of MRD.⁸,¹⁰,¹² As previously reported, males were overrepresented (64%) in our study.⁸,¹⁰,¹² The sex predilection observed is similar in human medicine.³⁷

The frequency of anemia, thrombocytopenia, azotemia, increase in liver enzyme activity, ionized hypercalcemia and Bence Jones proteinuria reported in our study was similar to previously studies.⁸⁻¹² Conversely, biclonal gammopathy was less frequent in our study (5%) compared with previous studies (20%-25%).⁸⁻¹⁰ However, a recent study did not report any biclonal gammopathy on SPE in 10 cats.¹² According to our results, it seems that biclonal gammopathy is infrequent. However, immunofixation electrophoresis would be required to confirm this finding.

Bone marrow plasmacytosis has been reported in 50% to 100% of cats with MRD.⁸⁻¹⁰,¹² In our study, BM plasmacytosis was diagnosed in 63% of cats, with one-third of cats having BM plasmacytosis of <10%. These results emphasize that BM plasmacytosis is uncommon in cats with MRD and that infiltration may be mild in many cases.¹,⁸,¹⁰,¹² In our study, 86% and 71% of cats had splenic and hepatic infiltration at diagnosis, respectively, confirming that visceral involvement is an important criterion for the diagnosis of MRD. Additionally, nonspecific ultrasonographic abnormalities were recorded in 61% and 89% of cats with confirmed splenic and hepatic infiltration, respectively. Thus, if MRD is suspected, splenic or hepatic ultrasound abnormalities or both are insufficient to establish a diagnosis. Cytology or histopathology or both are required to confirm involvement. In our study, normal abdominal ultrasonographic findings were recorded in 39% and 11% of cats with splenic and hepatic infiltration, respectively. This finding is consistent with previous studies in which a normal ultrasound examination could not rule out liver or spleen involvement.⁸⁻¹⁰,¹²

Osteolytic lesions were identified in 29% of cases, which is lower than previous studies (50%-66%).⁸,¹⁰ Differences in imaging modalities among studies do not explain this result, because staging was performed mainly by skeletal radiographs in previous studies as in our study. Although fine needle aspirates of osteolytic lesions were not performed in our study, plasma cell infiltration was suspected in cats with consistent radiographic lesions. Pathologic fracture seems to be infrequent, because only 2 cats were affected in our study, and 1 of 40 cats in 3 previous studies.⁸,¹⁰,¹² These results contrast with studies in humans, in which 80% of patients present with osteolytic lesions, osteoporosis or fractures on radiographs,⁵ and dogs, where 64% have osteolytic lesions and 2 of 38 dogs (5%) presented with pathologic fracture.¹ The lower sensitivity of radiography compared with CT, positron emission tomography-CT, and magnetic resonance imaging, which are used in human medicine, may decrease the sensitivity of lesion detection in dogs and cats.⁵,³⁸ As opposed to the previous study, osteolytic lesions were not associated with decreased MST in our study.⁸ Because CT and radiography were not routinely performed, osteolytic lesions may have been underdiagnosed, limiting rigorous statistical analysis.

In our cohort, the efficacy of melphalan or cyclophosphamide used in combination with prednisolone was similar to previously published data.¹² Cats treated with melphalan or cyclophosphamide had RR of 88% and 91%, respectively. Survival times for cats initially treated with melphalan or cyclophosphamide were not significantly
different. However, toxicity with the melphalan protocol was 3 times more frequent than with cyclophosphamide. These results were similar to a study where melphalan was more myelotoxic than cyclophosphamide.¹² Although melphalan was associated with a high RR in our study, its common BM toxicity led to its temporary discontinuation in 3 cats (15%). However, as has been recently demonstrated in dogs with MM, a pulsed protocol of melphalan could be less toxic than a continuous protocol in cats.¹³ In our study, hematologic abnormalities after chemotherapy initiation were suspected to be secondary to treatment. Cytopenia secondary to PD was considered less likely based on normal globulin concentration. Conversely, cyclophosphamide was well tolerated, and only 2 cats developed grade 2 neutropenia, and 1 cat developed grade 3 anemia. These results combined with those of a previous study emphasize that the toxicity associated with cyclophosphamide is mostly transient and does not require alteration in treatment protocols.¹² In our study, cats initially treated with chlorambucil and prednisolone had a satisfactory RR (100%) without toxicity. These results are similar to those of another study reporting mild and infrequent toxicity with chlorambucil.¹² However, the small number of cats treated with chlorambucil precludes conclusions about the toxicity and efficacy of this protocol.

In humans, bortezomib is a proteasome inhibitor that serves as the first-line drug for MM.³⁹ Although it is not currently widely available in veterinary medicine, it has been used in a cat that had a favorable response.⁴⁰ Additional studies evaluating toxicity and effectiveness in a larger cohort are needed.

In our study, fever and a history of recurrent respiratory signs were reported in 15% and 14% of cats, respectively. Fever was not reported at diagnosis of MRD in previous studies.⁸⁻¹⁰,¹² Respiratory signs have been reported in 6% to 20% of cases.¹⁰,¹² These findings may support concurrent immunosuppression. In our study, 1 cat was diagnosed with toxoplasmosis and another with mycoplasmosis at the time of diagnosis. Because these systemic infections often are associated with immunosuppression, we suspected that MRD may have more easily permitted development of infections. No cats developed an infection during chemotherapy. This finding is relevant because many cats treated with melphalan developed neutropenia. In contrast, other studies have described infections in cats during melphalan treatment, which led some authors to suggest the routine prescription of antibiotics.⁸,¹² The increased infection rate could be explained by the inhibition of normal plasma cell proliferation by neoplastic plasma cells and BM infiltration leading to leukopenia or chemotherapy-related immunosuppression.³,⁸,¹² In our study, only the 2 previously described cats received antibiotics. Because the risk of infection appeared to be low in our cohort, monitoring of cats with systemic MRD is recommended rather than systemic antibiotic prophylaxis.

Similar to other studies, the prognosis of cats with MRD in our cohort appears to be poor, with MST of 4 months.⁸,¹⁰ This result contrasts with other data documenting MST of 8 to 13 months.⁹,¹² However, these prolonged ST were only reported in 2 studies where cats were treated with cyclophosphamide or melphalan with exclusion of survival analysis of the cats not treated at all or treated with other protocols.⁹,¹² In addition, our survival analysis also included intent-

to-treat cats that were not treated for whatever reason. Those untreated cats could have decreased overall MST. When excluding cats that did not receive chemotherapy or were treated using protocols other than melphalan or cyclophosphamide in combination with prednisolone, the MST was 10.5 months in our cohort. Among cats with appropriate follow-up until death, death was attributed to MRD-related causes in 93% of cases. One cat died from arterial thromboembolism. Because no previous echocardiographic examination and no follow-up until death were available, it is not possible to rigorously attribute the arterial thromboembolism to MRD (HVS or hypercoagulability associated with protein-losing nephropathy), occult primary myocardopathy or other diseases. Another cat died of kidney failure. The progression of CKD was suspected to be the cause of death because this cat was diagnosed with CKD for several years and did not develop ionized hypercalcemia, pyelonephritis, HVS, Bence Jones proteinuria, or nephromegaly consistent with plasma cell infiltration during follow-up.

No prognostic factors associated with shorter ST have been established in cats diagnosed with MRD. One study grouped MRD into 2 categories (aggressive vs nonaggressive) based on criteria known to predict behavior in dogs.⁸ These results should be approached with caution because the cohort only consisted of 9 cats.⁸ Our study is the first to establish factors associated with shorter ST based on multivariate analysis in a large cohort. Because, at the time of writing, no established cutoffs for AGR, NLR, PLR, and hyperglobulinemia are available for cats diagnosed with MRD, tertile values were used as cutoffs to assess the association with some variables. Tertile values were preferred to quartile values to ensure a sufficient number of cases to obtain reliable results for statistical analysis. Tertile values were preferred to other methods (such as receiver operating curve analysis) to limit the influence of the second variable in determination of cutoffs. Because a low AGR could reflect more aggressive disease, the first tertile was chosen as a cutoff. High NLR¹³,²⁷⁻³² was demonstrated to be a negative prognostic factor in humans and dogs with MM and high PLR³¹,³² in humans. Therefore, the second tertile was chosen for NLR,¹³,²⁷⁻³² PLR,³¹,³² and hyperglobulinemia.

In a recent study, cats with MRD that were anemic at the time of diagnosis had a shorter MST (252 days) than nonanemic cats (289 days).¹² The difference in MST between the 2 groups was not significant. In our study, anemia and thrombocytopenia were significantly and independently associated with shorter ST. Anemia and thrombocytopenia were defined according to the RI of the participating institutions. The RI for anemia (30%) was similar across all institutions. Because the RI for platelet count was different among institutions, individual laboratory RI was chosen. In 1 multicenter study, anemia was defined as a hematocrit <25%.⁹ Other non-multicentric studies used cutoffs of 29.5%¹² or 31.7%¹⁰ for anemia and 110 × 10⁹/L¹² or 175 × 10⁹/L¹⁰ for thrombocytopenia. Despite the fact that thrombocytopenia was defined by different cutoffs in our study, it appears that the median and range of platelet count of thrombocytopenic cats were within the cutoffs defined by other studies. In previous studies, neither anemia nor thrombocytopenia were associated with worse outcome in dogs with MM.¹,¹³,¹⁴ Conversely, anemia is also a recognized negative
prognostic factor in humans with MM.<sup>33-35</sup> The worse outcomes associated with anemia and thrombocytopenia could be related to severe BM infiltration, blood loss secondary to HVS or gastrointestinal bleeding or both. In our study, gastrointestinal bleeding was not recorded. Gastrointestinal bleeding was documented in 20% of dogs with MM.<sup>41</sup> Recently, a case of MM involving the gastrointestinal tract was reported in a dog.<sup>42</sup> Thus, cats with MRD and evidence of gastrointestinal bleeding may have gastrointestinal plasma cell infiltration. Anemia also may result from chronic illness, causing anemia of chronic disease and erythrophagocytosis.<sup>43,44</sup> Thrombocytopenia may result from viral diseases, disseminated intravascular coagulation, immune-mediated thrombocytopenia, and thrombotic thrombocytopenic purpura.<sup>45-49</sup> Considering the guarded prognosis associated with those diseases, it may worsen the prognosis.

In a previous study, cats presenting with hypoalbuminemia at diagnosis had a more than 3-fold longer ST (684 days) than cats with normal albumin concentration (214 days).<sup>12</sup> The risk of death for cats with normal albumin concentration vs hypoalbuminemia approached statistical significance, but a type II error may have affected the outcome.<sup>12</sup> This result contrasts with our findings, which supported hypoalbuminemia and low AGR as variables significantly associated with shorter ST in the univariate analysis. This association was not significant after multivariate analysis, which may be a result of the small sample size. In dogs, neither hypoalbuminemia nor low AGR has been associated with shorter ST.<sup>1,13,14</sup> Several studies have shown that hypoalbuminemia is a negative prognostic factor in people with MM,<sup>50-52</sup> The specific cause of decreased serum albumin concentrations in MM is unknown. Some studies report that low serum albumin concentrations correlate with increased serum concentrations of interleukin-6, a potent plasma cell growth factor reflecting disease severity and cell proliferation.<sup>53-64</sup> Low serum albumin concentrations also may be related to prolonged dysrexia.<sup>65</sup> In human medicine, 1 study reported that patients with hypoalbuminemia were older and had lower hemoglobin concentrations, worse performance status, and higher concentrations of serum beta2-microglobulin, serum M protein, and BM plasma cells.<sup>50</sup> Because those clinical factors reflect disease severity in MM patients, hypoalbuminemia in cats also could be linked to a more severe disease course.

Our study had some limitations, mainly related to its multicenter retrospective nature. Despite being the largest study published, the population size is small and not homogeneous in terms of staging tests and modalities, initial treatment, follow-up, and rescue therapy. Moreover, immunofixation electrophoresis was not performed at diagnosis, and the response to treatment was only based on serum globulin measurements. A recent study in dogs found that assessing response based on serum M-protein concentration was associated with both specific clinical events and OST, whereas categorization based on serum globulin concentration was not.<sup>66,67</sup> These results led to the recommendation of the use of electrophoresis-based techniques with evaluation of densitometric protein as a means of monitoring animals with secretory MRD. Furthermore, osteolytic lesions and Bence Jones proteinuria were not reassessed during follow-up. The variability in the reevaluation schedule could have led to calculation of a longer time to response than justified. Finally, the diagnosis of HVS only relied on clinical signs, and it would

have been more reliable to perform measurements of blood viscosity and exclude other pathologies.

In conclusion, our findings suggest that MRD in cats manifests more frequently as hepatic or splenic infiltration than marked BM plasmacytosis and has a poor prognosis. Cyclophosphamide and corticosteroids as first-line treatment appear to be well tolerated and, in our study, had no significant difference in MST compared to melphalan, although lack of a significant difference could have been related to small sample size. The estimated overall MST was 122 days. However, the MST of cats treated with melphalan or cyclophosphamide plus corticosteroids as initial treatment was 315 days.

Anemia and thrombocytopenia were found to be significantly and independently associated with shorter ST. Additional studies are warranted to validate the negative prognostic value of these markers in a larger number of cases.

### ACKNOWLEDGMENT

No funding was received for this study. Part of this work was presented as an oral presentation at the 2023 European College of Veterinary Internal Medicine - Companian Animals (ECVIM-CA) Congress, Barcelona, Spain. The authors acknowledge Dr Morgane Canonne, Dr Manon Delaunay, Dr Quentin Fournier, Dr Juan Carlos Serra and Dr Cyril Winter for their contribution to this study. The authors also acknowledge Pr. David Killick for his contribution to this study and his institutional animal care and use committee.

### CONFLICT OF INTEREST DECLARATION

Authors declare no conflict of interest.

### OFF-LABEL ANTIMICROBIAL DECLARATION

Authors declare no off-label use of antimicrobials.

### INSTITUTIONAL ANIMAL CARE AND USE COMMITTEE (IACUC) OR OTHER APPROVAL DECLARATION

Approved by Comité d'éthique en Recherche Clinique (ComERC) Ecole nationale vétérinaire d'Alfort, number 2022-10-13 and by Veterinary Research Ethics Committee of Institute of Infection, Veterinary and Ecological Sciences, Leahurst Campus, Neston, South Wirral, reference VREC1265.

### HUMAN ETHICS APPROVAL DECLARATION

Authors declare human ethics approval was not needed for this study.

### ORCID

Sarah Benjamin https://orcid.org/0000-0001-9475-4492

Matthew Kornya https://orcid.org/0000-0002-5928-9262

Ghita Benchekroun https://orcid.org/0000-0003-3947-5655

Jérémy Béguin https://orcid.org/0000-0003-2400-8309

### REFERENCES

1. Vail DM. Myeloma-related disorders. In: Withrow SJ, Vail DM, eds. *Small Animal Clinical Oncology*. 6th ed. St. Louis: Saunders Elsevier; 2020:739-772.
2. Engle G, Brodey R. A retrospective study of 395 feline neoplasms. *J Am Anim Hosp Assoc*. 1969;5:21-31.

3. MacEwen EG, Hurvitz Al. Diagnosis and management of monoclonal gammopathies. *Vet Clin North Am*. 1977;7:119-132.

4. Bird JM, Owen RG, D'Sa S, et al. Guidelines for the diagnosis and management of multiple myeloma 2011. *Br J Haematol*. 2011;154:32-75.

5. International Myeloma Working Group. Criteria for the classification of monoclonal gammopathies, multiple myeloma and related disorders: a report of the International Myeloma Working Group. *Br J Haematol*. 2003;121:749-757.

6. Drazner F. Multiple myeloma in the cat. *Comp Contin Educ Pract Vet*. 1982;4:206-216.

7. King A, Davies D, Irwin P. Feline multiple myeloma: literature review and four case reports. *Aust Vet Pract. 2002;32:146-151.

8. Hanna F. Multiple myelomas in cats. *J Feline Med Surg*. 2005;7:275-287.

9. Mellor PJ, Haugland S, Murphy S, et al. Myeloma-related disorders in cats commonly present as extramedullary neoplasms in contrast to myeloma in human patients: 24 cases with clinical follow-up. *J Vet Intern Med*. 2006;20:1376-1383.

10. Patel RT, Caceres A, French AF, McManus PM. Multiple myeloma in 16 cats: a retrospective study. *Vet Clin Pathol*. 2005;34:341-352.

11. Mellor PJ, Haugland S, Smith KC, et al. Histopathologic, immunohistochemical, and cytologic analysis of feline myeloma-related disorders: further evidence for primary extramedullary development in the cat. *Vet Pathol*. 2008;45:159-173.

12. Cannon CM, Knudson C, Borgatti A. Clinical signs, treatment, and outcome in cats with myeloma-related disorder receiving systemic therapy. *J Am Anim Hosp Assoc*. 2015;51:239-248.

13. Fernández R, Chon E. Comparison of two melphalan protocols and evaluation of outcome and prognostic factors in multiple myeloma in dogs. *J Vet Intern Med*. 2018;32:1060-1069.

14. Matus R, Leifer C, MacEwen E, Hurvitz Al. Prognostic factors for multiple myeloma in the dog. *J Am Vet Med Assoc*. 1986;188:1288-1292.

15. Hanbali A, Hassanein M, Rasheed W, Aljurf M, Alsharif F. The evolution of prognostic factors in multiple myeloma. *Adv Hematol*. 2017;2017:1-11.

16. Palumbo A, Anderson K. Multiple myeloma. *N Engl J Med*. 2011;1046:10-1060.

17. Smith D, Yong K. Advances in understanding prognosis in myeloma. *Br J Haematol*. 2016;175:367-380.

18. Basit A, Siddiqui N, Hameed A, et al. Factors affecting outcome of patients with multiple myeloma. *J Ayub Med Coll Abbottabad*. 2014;26:376-379.

19. Knudsen LM, Hjorth M, Hippe E, Nordic Myeloma Study Group. Renal failure in multiple myeloma: reversibility and impact on the prognosis. *Eur J Haematol*. 2000;65:175-181.

20. Augustson BM, Begum G, Dunn JA, et al. Early mortality after diagnosis of multiple myeloma: analysis of patients entered onto the United Kingdom Medical Research Council trials between 1980 and 2002—Medical Research Council Adult Leukaemia Working Party. *Clin Oncol*. 2005;23:9219-9226.

21. Dimopoulos M, Kastritis E, Rosinol L, et al. Pathogenesis and treatment of renal failure in multiple myeloma. *Leukemia*. 2008;22:1485-1493.

22. Haynes RJ, Read S, Collins GP, Darby SC, Winearls CG. Presentation and survival of patients with severe acute kidney injury and multiple myeloma: a 20-year experience from a single centre. *Nephrol Dial Transplant*. 2010;25:419-426.

23. Heher EC, Rennke HG, Laubach JP, Richardson PG. Kidney disease and multiple myeloma. *Clin J Am Soc Nephrol*. 2013;8:2007-2017.

24. Knudsen LM, Hippe E, Hjorth M, Holmberg E, Westin J. Renal function in newly diagnosed multiple myeloma—a demographic study of 1353 patients. *Eur J Haematol*. 1994;53:207-212.

25. Leung N, Nasr SH. Myeloma-related kidney disease. *Adv Chronic Kidney Dis*. 2014;21:36-47.

26. Ríos-Tamayo R, Sánchez MJ, Puerta JM, et al. Trends in survival of multiple myeloma: a thirty-year population-based study in a single institution. *Cancer Epidemiol*. 2015;39:693-699.

27. Kelkitli E, Atay H, Çilingir F, et al. Predicting survival for multiple myeloma patients using baseline neutrophil/lymphocyte ratio. *Ann Hematol*. 2014;93:841-846.

28. Li Y, Li H, Li W, et al. Pretreatment neutrophil/lymphocyte ratio but not platelet/lymphocyte ratio has a prognostic impact in multiple myeloma. *J Clin Lab Anal*. 2017;31:e22107.

29. Onec B, Okutan H, Albayrak M, et al. The predictive role of the neutrophil/lymphocyte ratio in survival with multiple myeloma: a single center experience. *J Clin Lab Anal*. 2017;31:e22032.

30. Romano A, Parrinello N, Consoli M, et al. Neutrophil to lymphocyte ratio (NLR) improves the risk assessment of ISS staging in newly diagnosed MM patients treated upfront with novel agents. *Ann Hematol*. 2015;94:1875-1883.

31. Shi L, Qin X, Wang H, et al. Elevated neutrophil-to-lymphocyte ratio and monocyte-to-lymphocyte ratio and decreased platelet-to-lymphocyte ratio are associated with poor prognosis in multiple myeloma. *Oncotarget*. 2017;8:18792-18801.

32. Wongrakpanich S, George G, Chaiwatcharayut W, et al. The prognostic significance of neutrophil-to-lymphocyte and platelet-to-lymphocyte ratios in patients with multiple myeloma. *J Clin Lab Anal*. 2016;30:1208-1213.

33. Anagnostopoulos A, Gika D, Symeonidis A, et al. Multiple myeloma in elderly patients: prognostic factors and outcome. *Eur J Haematol*. 2005;75:370-375.

34. Iriuchishima H, Saitoh T, Handa H, et al. A new staging system to predict prognosis of patients with multiple myeloma in an era of novel therapeutic agents. *Eur J Haematol*. 2015;94:145-151.

35. Yusuf AA, Natwick T, Werther W, et al. A retrospective analysis to examine factors associated with mortality in Medicare beneficiaries newly diagnosed with multiple myeloma. *Curr Med Res Opin*. 2016;32:1989-1996.

36. Veterinary cooperative oncology group – common terminology criteria for adverse events (VCOG-CTCAE) following chemotherapy or biological antineoplastic therapy in dogs and cats v1.1. Vet Comp Oncol. 2016;14:417-446.

37. Kyle RA, Gertz MA, Witzig TE, et al. Review of 1027 patients with newly diagnosed multiple myeloma. *Mayo Clin Proc*. 2003;78(1):21-33.

38. Rajkumar SV, Dimopoulos MA, Palumbo A, et al. International Myeloma Working Group updated criteria for the diagnosis of multiple myeloma. *Lancet Oncol*. 2014;15:e538-e548.

39. Moreau P, San Miguel J, Ludwig H, et al. Multiple myeloma: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. *Ann Oncol*. 2013;24(Suppl 6):vi133-vi137.

40. Tani H, Miyamoto R, Miyazaki T, Oniki S, Tamura K, Bonkobara M. A feline case of multiple myeloma treated with bortezomib. BMC Vet Res. 2022;18(1):384.

41. Caldin M, Campigli M, Zoia A, et al. Bleeding diathesis in canine multiple myeloma and prognostic implications: a cohort study in 156 dogs. *Res Vet Sci*. 2019;125:305-308.

42. Roberts E, Shirlow A, Cox A, Davies O. Multiple myeloma involving the gastrointestinal tract in an English Springer Spaniel. *Vet Med Sci*. 2022;8:2273-2276.

43. Dunbar MD, Lyles S. Hemophagocytic syndrome in a cat with multiple myeloma. *Vet Clin Pathol*. 2013;42(1):55-60.

44. Webb J, Chary P, Northrup N, Almy F. Erythrophagocytic multiple myeloma in a cat. *Vet Clin Pathol*. 2008;37(3):302-307.

45. Jordan HL, Grindem CB, Breitschwerdt EB. Thrombocytopenia in cats: a retrospective study of 41 cases. *J Vet Intern Med*. 1993;7(5):261-265.
46. Gupta V, Hegde UM, Parameswaran R, Newland AC. Multiple myeloma and immune thrombocytopenia. *Clin Lab Haematol.* 2000;22(4):239-242.

47. Xiao X, Zhong HY, Zhang GS, Deng MY. Thrombotic thrombocytopenic purpura as initial and major presentation of multiple myeloma. *J Thromb Thrombolysis.* 2013;36:422-423.

48. Hofmeister CC, Jin M, Cataland SR, Benson DM, Wu HM. TTP disease course is independent of myeloma treatment and response. *Am J Hematol.* 2010;85(4):304-306.

49. Alpay N, Uzun S, Bahat G, Yavuz S, Erten N, Tascioglu C. Thrombotic thrombocytopenic purpura associated with multiple myeloma. *Blood Coagul Fibrinolysis.* 2008;19(5):439-441.

50. Kim JE, Yoo C, Lee DH, Kim SW, Lee JS, Suh C. Serum albumin level is a significant prognostic factor reflecting disease severity in symptomatic multiple myeloma. *Ann Hematol.* 2010;89:391-397.

51. Shin S-J, Roh J, Kim M, et al. Prognostic significance of absolute lymphocyte count/absolute monocyte count ratio at diagnosis in patients with multiple myeloma. *Korean J Pathol.* 2013;47:526-533.

52. Chen Y-H, Magalhaes MC. Hypoalbuminemia in patients with multiple myeloma. *Arch Intern Med.* 1990;150:605-610.

53. Bataille R, Jourdan M, Zhang X-G, Klein B. Serum levels of interleukin 6, a potent myeloma cell growth factor, as a reflect of disease severity in plasma cell dyscrasias. *J Clin Investig.* 1989;84:2008-2011.

54. Bjerrum OW, Plesner T. Beta-2-microglobulin: a valuable parameter of stage, prognosis and response to treatment in myelomatosis. *Scand J Haematol.* 1985;35:22-25.

55. Cuzick J, De Stavola B, Cooper E, et al. Long-term prognostic value of serum β2 microglobulin in myelomatosis. *Br J Haematol.* 1990;75:506-510.

56. Dawson AA, Ogston D. Factors influencing the prognosis in myelomatosis. *Postgrad Med J.* 1971;47:635-638.

57. Durie BG, Salmon SE. A clinical staging system for multiple myeloma correlation of measured myeloma cell mass with presenting clinical features, response to treatment, and survival. *Cancer.* 1975;36:842-854.

58. Durie B, Stock-Novack D, Salmon SE, et al. Prognostic value of pretreatment serum beta 2 microglobulin in myeloma: a Southwest Oncology Group Study. *Blood.* 1990;75:823-830.

59. Ershler WB, Keller ET. Age-associated increased interleukin-6 gene expression, late-life diseases, and frailty. *Annu Rev Med.* 2000;51:245-270.

60. Fonseca R, San MJ. Prognostic factors and staging in multiple myeloma. *Hematol Oncol Clin North Am.* 2007;21:1115-1140.

61. Greipp PR, Miguel JS, Durie BG, et al. International staging system for multiple myeloma. *Clin Oncol.* 2005;23:3412-3420.

62. Jacobson JL, Hussein MA, Barlogie B, Durie BG, Crowley JJ, Southwest Oncology Group. A new staging system for multiple myeloma patients based on the Southwest Oncology Group (SWOG) experience. *Br J Haematol.* 2003;122:441-450.

63. Kapoor P, Snozek CL, Colby C, et al. Clinical impact of discordance in serum albumin measurements on myeloma international staging system. *Clin Oncol.* 2008;26:4051-4052.

64. Lichtenstein A, Tu Y, Fady C, Vescio R, Berenson J. Interleukin-6 inhibits apoptosis of malignant plasma cells. *Cell Immunol.* 1995;162:248-255.

65. Sullivan DH. Guest editorial: what do the serum proteins tell us about our elderly patients? *J Gerontol Biol Sci.* 2001;56:M71-M74.

66. Moore AR, Harris A, Jeffries C, Avery PR, Vickery K. Retrospective evaluation of the use of the International Myeloma Working Group response criteria in dogs with secretory multiple myeloma. *J Vet Intern Med.* 2021;35:442-450.

67. Kumar S, Paiva B, Anderson KC, et al. International Myeloma Working Group consensus criteria for response and minimal residual disease assessment in multiple myeloma. *Lancet Oncol.* 2016;17:e328-e346.

**How to cite this article:** Lecot L, Desmas-Bazelle I, Benjamin S, et al. Descriptive analysis and prognostic factors in cats with myeloma-related disorders: A multicenter retrospective study of 50 cases. *J Vet Intern Med.* 2024;38(3):1693-1705. doi:10.1111/jvim.17051