Circulating aberrant plasma cells allow risk stratification of patients with myeloma
Authors: Adela Periago, José A. Campillo, Anna Mrowiec, Lourdes Gimeno, Natividad R. Montes, María V. Martínez‐Sánchez, Valentin Cabañas‐Perianes, Carmen García‐Garay, José M. Bolarin, Adela Blasco‐Mogorrón, Manuel Muro, Mercedes Berenguer, José M. Moraleda, García‐Alonso •••, Alfredo Minguela
Journal: American Journal of Hematology (2016)

To the Editor: Plasma cell (PCs) disorders (PCDs) include benign [monoclonal gammopathy of uncertain significance (MGUS)] and malignant [smoldering multiple myeloma (SMM) and multiple myeloma (MM)] forms. New therapies have improved the outcome of MM patients, but with considerable heterogeneity 1, 25% of patients survive 2 years or less, so that risk stratification is becoming an important issue in the management of myeloma. Prognostic biomarkers such as age, international staging system (ISS), based on serum albumin and beta-2 microglobulin 2 and the reviewed-ISS including lactate dehydrogenase (LDH) 3, complemented by chromosomal abnormalities (CA), offer robust risk stratification models 3, 4. Circulating aberrant-PCs (aPC) have been described as an adverse independent prognostic factor in MGUS, SMM, and MM 5. This work investigates the diagnostic and prognostic value of circulating-aPCs, at diagnosis, on 86 MGUS and 72 MM (17 patients were initially diagnosed as SMM, but re-classified as MM following new criteria of the International Myeloma Working Group (IMWG) 6) Caucasian patients, treated afterwards mostly (85%) with novel therapies. Patients were recruited at Virgen de la Arrixaca, Rafael Mendez, and Santa Lucía Hospitals in Murcia, Spain. Risk stratification of MM patients was done following: (a) 2014-IMWG criteria 4, low-risk (age < 55, ISS-I/II and standard-risk CA), high-risk (ISS-II/III and P53-deletion, t(4;14) and/or 1q-amplification) and intermediate-risk (remaining patients); and (b) 2015-IMWG criteria 3, low-risk (ISS-I, standard-risk CA and normal-LDH), high-risk (ISS-III and either high-LDH or P53-deletion, t(4;14) and/or t(14;16)) and intermediate-risk (remaining patients). Further details for clinical/biological patient endpoints, PC-immunophenotyping (Supporting Information Fig. s1), FISH, MM therapy and statistics are described in Supporting Information (Supporting Information Table sI). The diagnostic utility of circulating-aPCs to differentiate MGUS from MM was assessed by ROC-curve (Supporting Information Fig. s2), with area under the curve = 0.784, cut-off = 0.0035% aPC, sensitivity = 65.0% and specificity = 89.5%. The frequency of patients with circulating-aPCs > 0.0035% was 7.0% (6/86) in MGUS and 55.6% in MM (40/72, OR = 16.66, P < 0.01 × 10−10). Progressive disease in the three-year follow-up was observed in 3 out of 86 MGUS (1.16% per year) and in 37 out of 72 MM (17.13% per year). Circulating-aPC ≥ 0.0035% in MM negatively impacted the three-year disease progression (3yDP, 65.0% vs. 34.4%, P < 0.01) and the three-year overall survival (3yOS, 52.5% vs. 90.6%, P < 0.001) compared with patients showing circulating-aPC < 0.0035%. Presence of circulating-aPC ≥ 0.0035% negatively impacted the 3yOS irrespective of the therapy used, but very significantly for therapies based on bortezomib, thalidomide, and/or lenalidomide (51.6% vs. 94.7%, P <0.001), including auto-stem cell transplantation (ASCT) (69.2% vs. 100%, P = 0.09) or not (36.4% vs. 75.0%, P < 0.05) (Supporting Information Fig. s3). The prognostic utility of circulating-aPC evaluation encouraged us to explore its ability to complement IMWG risk stratification models, and even to propose a new model, based exclusively on blood parameters (Fig. 1). In our model, adverse cytogenetic was replaced by circulating-aPC ≥ 0.0035% and low-risk age increased from 55 up to 65. Although the 3yDP rates for the IMWG-2014, IMWG-2015, and circulating-aPC models for patients at low-risk (42.9%, 29.4% and 29.4%), intermediate-risk (41.7%, 56.9% and 40.9%), and high-risk (82.4%,75.0% and 69.7%) and the 3yOS rates for low-risk (100%, 82% and 100%), intermediate-risk (70.1%, 64.7% and 72.7%), and high-risk (52.9%, 50.0% and 51.5%) were mostly comparable, distribution of MM patients between the low, intermediate, and high risk groups produced by the circulating-aPC model (low = 17, intermediate = 22 and high = 33) was statistically more significant (P < 0.01 vs. P < 0.02 and P = 0.079 for the 3yDP, and P < 0.001 vs. P < 0.05 and P = 0.053 for the 3yOS) and clinically more relevant than those offered by the 2014-IMWG (low = 7, intermediate = 48, and high = 17) and the 2015-IMWG (low = 17, intermediate = 51, and high = 4) models. The circulating-aPC model duplicates and multiplies by 8 (33 vs. 17 and 4) the numbers of high-risk patients compared to 2014- and 2015-IMWG models, respectively; halves the number of intermediate-risk (22 vs. 48 and 51); and identifies at least as many low-risk patients (17 vs. 17 and 7) as the IMWG models. Indeed, our model perfectly complemented IMWG's based on cytogenetic (Fig. 1D), such that it was able to reclassify 23% (4/17) and 25% (1/4) from the high-risk 2014 and 2015 IMWG-models into low-risk or intermediate-risk circulating-aPC model; 58% (28/48) and 72.5% (37/51) from the intermediate-risk 2014 and 2015 IMWG-models into low-risk or high-risk circulating-aPC-model; and 14% (1/7) and 41% (7/17) from the low-risk 2014 and 2015 IMWG-models into intermediate-risk or high-risk circulating-aPC model. The 3yOS rates for re-classified patients are shown in Fig. 1. Cox regression multivariate analysis (Supporting Information Table sII) confirmed that the circulating-aPC model has independent prognostic value and higher predictive capacity than the IMWG's, both for the progression of the disease (OR = 1.745, P < 0.05) and the 3yOS (OR = 3.156, P < 0.01). Risk stratification of multiple myeloma patients following 2014 and 2015 IMWG models and a new model based on ciculating aPC. Kaplan–Meier analysis of disease progression and patient OS for risk groups set following 2014 (A) 4 and 2015 (B) 3 IMWG models and a new model (C) based on similar criteria than those described in (A), but changing the presence of unfavorable chromosomal abnormalities (CA) for the presence of circulating-aPC ≥ 0.0035% and the age for low risk from 55 to 65 years. Statistical significance estimated by the long-rank test is shown. Pie charts represent distribution of MM patients in the low (white), intermediate (gray), and high (black) risk groups in each model. D: Risk re-stratification of low, intermediate, and high risk patients from the 2014 and 2015 IMWG models, following the criteria of the circulating-aPC model. Bars represent number of MM patients reclasified into the low (white), intermediate (gray), and high (black) risk circulating-aPC groups. Percentages indicate the OS of each re-classified sub-group. nLDH, normal levels of LDH; hLDH, high levels of LDH. Our data show that it is possible to establish a cut-off of 0.0035% for circulating-aPCs evaluated by multi-parametric flow cytometry, which offers high sensitivity and a specificity to discriminate MGUS from MM. Obviously, the sensitivity and specificity of this analysis by itself is not enough to offer a definitive diagnosis, but might complement clinical evidences, which all together can help to achieve accurate diagnoses with a simple blood test in half an hour. More importantly, this cut-off can also help to discriminate two prognostic groups of myeloma patients. Patients with values of circulating-aPCs ≥ 0.0035% show unfavorable outcome, with higher progression rates and decreased 3yOS. Other studies have reported the independent prognostic value of circulating-aPCs in PCD 5. However, despite its great prognostic capacity, simplicity, and economy, analysis of circulating-aPCs has not been incorporated into clinical practice yet. This is even more surprising considering that its predictive value is maintained regardless the type of treatment, including modern therapies based on bortezomib, thalidomide, and/or lenalidomide or the inclusion of ASCT. In the light of these results, a risk stratification model for patients with MM based exclusively on blood parameters is proposed. Patients are stratified following similar criteria to those of the 2014-IMWG model 4, but substituting adverse cytogenetic by the presence of circulating-aPC > 0.0035%. All models, including the 2014-IMWG, 2015-IMWG, and the one based on circulating-aPCs, offer comparable three-year progression and OS rates for low, intermediate, and high risk groups. However, compared to the IMWG models, the high sensitivity of multi-parametric flow cytometry to detect very low number of circulating-aPCs, maximize the number of patients to be included in the high-risk (45% vs. 23.6% and 5.5%) and the low-risk (23.6% vs. 9.7% and 23.6%) and minimize the intermediate-risk (30.5% vs. 62.5% and 70.8%). Although models based on cytogenetic are the most established in clinical practice 3, 4, the low frequency of unfavorable CA detected by FISH, even using purified PCs, leads to the inclusion of most patients in the intermediate-risk group, and therefore to a great uncertainty to point out personalized risk-adapted therapies. The model based on circulating-aPCs offer the opportunity to assign better stratification to 45.8% and 62.5% of the 2014-IMWG and 2015-IMWG risk groups, respectively, which could prevent these misclassified patients from under- or over-treatment. The increasing incidence of PCDs in western countries makes necessary to have fast and economical methods to guide the discrimination between benign and malignant forms and to detect patients at high-risk of progression and death, thereby offering the opportunity to provide personalized risk-adapted therapies for rationalizing the cost of drugs, toxicities, and efficacies. Our results suggest that the evaluation of circulating-aPC by flow cytometry might provide a risk stratification model useful in the clinical managemente of MM under modern therapies. Authors thank Pastora Céspedes and Florentina Villar for technical assistance, as well as the hematologist from the hematology services from Clinic University Hospital Virgen de la Arrixaca (Murcia, Spain), Rafael Mendez Hospital (Lorca, Spain) and University Hospital Santa Lucía (Cartagena, Spain) for their kind collaboration in enrolling patients. Adela Periago,1 José A. Campillo,2 Anna Mrowiec,2 Lourdes Gimeno,2Natividad R. Montes,2 María V. Martínez-Sánchez,2 Valentin Cabañas-Perianes,3Carmen García-Garay,4 José M. Bolarin,2 Adela Blasco-Mogorrón,2 Manuel Muro,2 Mercedes Berenguer,3 José M. Moraleda,3 Ana M. García-Alonso,2 Alfredo Minguela2* 1Hematology Service, Hospital Rafael Méndez, Lorca, Murcia, Spain 2Immunology Service, Instituto Murciano De Investigación Biosanitaria (IMIB) and Centro De Investigación Biomédica En Red De Enfermedades Hepáticas Y Digestivas (CIBERehd), Hospital Clínico Universitario Virgen De La Arrixaca (HCUVA), Murcia, Spain 3Hematology Service, IMIB, HCUVA, Murcia, Spain 4Hematology Service, Hospital General Universitario Santa Lucía, Cartagena, Murcia, Spain Additional Supporting Information may be found in the online version of this article. Supporting Information Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.