Myelodysplastic/myeloproliferative neoplasms with ring sideroblasts and thrombocytosis (MDS/MPN-RS-T): Mayo-Moffitt collaborative study of 158 patients

<jats:title>Abstract</jats:title><jats:p>The current World Health Organization (WHO) classification of myeloid malignancies includes myelodysplastic/myeloproliferative neoplasms with ring sideroblasts and thrombocytosis (MDS/MPN-RS-T) as a distinct entity. Previous literature on predictors of survival was based on the provisional category of refractory anemia with ring sideroblast and thrombocytosis (RARS-T), which was not subject to MDS/MPN-RS-T exclusionary criteria such as PB blast% ≥1, BM blast% ≥5 or cytogenetic abnormalities such as t(3;3)(q21.2;q26.2), inv(3)(q21.23q26.2) or isolated del(5q). We examined overall (OS) and leukemia-free (LFS) survival and its predictors, among 158 patients with WHO-defined MDS/MPN-RS-T. In univariate analysis, age ≥70 years (<jats:italic>P</jats:italic> = 0.006), hemoglobin (Hb) ≤10 g/dL (<jats:italic>P</jats:italic> = 0.03) and abnormal karyotype (excluding -Y, <jats:italic>P</jats:italic> = 0.008) were associated with shortened OS, which was otherwise not affected by either <jats:italic>ASXL1</jats:italic> (<jats:italic>P</jats:italic> = 0.7), <jats:italic>SF3B1 (P</jats:italic> = 0.4<jats:italic>)</jats:italic> or <jats:italic>JAK2</jats:italic> V617F <jats:italic>(P</jats:italic> = 0.7<jats:italic>)</jats:italic> mutations; in multivariable analysis, Hb ≤ 10 g/dL (<jats:italic>P</jats:italic> = 0.03) and abnormal karyotype (<jats:italic>P</jats:italic> = 0.001) remained significant, and thus allowed the development of an operational survival model with low (0 risk factors, median OS 10.5 years), intermediate (1 risk factor, median OS 4.8 years) and high risk (2 risk factors, median OS 1.4 years) categories (<jats:italic>P</jats:italic> = 0.0009). Comparison of MDS/MPN-RS-T (<jats:italic>n</jats:italic> = 158) and MDS/MPN-U with BM RS ≥ 15% (MDS/MPN-U-RS; <jats:italic>n</jats:italic> = 25) did not reveal significant differences in frequency of thrombosis, OS, or LFS, although <jats:italic>SF3B1</jats:italic> mutation frequency was higher in the former (93% versus 59%; <jats:italic>P</jats:italic> = 0.0005). These data suggest limited survival impact for molecular abnormalities and the morphological distinction between MDS/MPN-RS-T and MDS/MPN-U-RS.</jats:p>

section_content: The 2016 World Health Organization (WHO) revision of myeloid malignancies and its recent iteration included patients with myelodysplastic/myeloproliferative neoplasms with ring sideroblasts and thrombocytosis (MDS/MPN-RS-T) as a distinct entity, under the MDS/MPN category [1, 2]. Previously, these patients were included under the provisional MDS/MPN category of refractory anemia with ring sideroblasts and thrombocytosis (RARS-T) [3, 4]. MDS/MPN-RS-T is distinguished from myelodysplastic syndrome with ring sideroblasts (MDS-RS) by the presence of thrombocytosis (platelet count ≥450 × 10 9 /L) and bone marrow (BM) megakaryocyte morphology similar to that seen in MPN. MDS/MPN-RS-T is in addition characterized by presence of SF3B1 mutations in 60-90% of patients and JAK2 V617F in a smaller percentage [1, [5] [6] [7] [8] [9] [10]. In order to be classified under the MDS/MPN-RS-T category, patients should also meet certain exclusionary criteria such as BM blast% ≥5, peripheral blood (PB) blast% ≥1, and cytogenetic abnormalities such as t(3; 3) (q21. 3; q26. 2), inv(3) (q21. 3; q26. 2) or isolated del(5q), or the BCR/ABL1 fusion oncogene [1, 11]. Of note, suspected cases with ≥15% BM RS and ≥1% PB or ≥5% BM blasts are classified as MDS/MPN-unclassifiable (MDS/MPN-U), while cases with leukocytosis [white blood cell (WBC) count of ≥13 × 10 9 /L] might be included in the category of MDS/MPN-RS-T, even in the absence of thrombocytosis. 

We have previously reported data from a large cohort of patients (n = 135) with MDS/MPN-U and found that patients with BM RS ≥ 15% (n = 13) had better outcomes than those with BM RS < 15% (n = 103), but similar outcomes when compared to patients with MDS/MPN-RS-T patients (n = 72) [12]. The analysis was however limited by small sample size and differential follow-up between the two groups. Nonetheless, these data call into question the necessity of a strict MDS/MPN-RS-T definition based on the aforementioned criteria and highlight its limitations. The objectives of the current study were to (i) define the natural history of MDS/MPN-RS-T, including determination of long-term survival and prognostic factors, and (ii) formally compare clinical and prognostic features between a larger cohort of patients with MDS/MPN-RS-T (n = 158) and MDS/MPN-U with ≥15% BM RS (MDS/MPN-U-RS), but not meeting criteria for MDS/MPN-RS-T (n = 25), so as to inform future revisions of the WHO classification of myeloid malignancies.
section_name: INTRODUCTION

section_content: Clinical and pathologic data from consecutive adult patients with WHOdefined MDS/MPN-RS-T (n = 158) and MDS/MPN-U-RS (n = 25) were collected from two major institutions, Mayo Clinic (Rochester, Minnesota) and H. Lee Moffitt Cancer Center (Tampa, Florida) after institutional review board (IRB) approval at each institution. Diagnostic BM biopsy reports were carefully reviewed to ensure compliance with the latest WHO criteria. The MDS/MPN-U-RS patients did not meet MDS/MPN-RS-T criteria due to PB blast% >1 (n = 9), BM blast% >5 (n = 8), and the rest due to absence of thrombocytosis. There were 3 MDS/MPN-U-RS patients who did not have thrombocytosis or leukocytosis but were classified as such since they did not meet diagnostic requirements of any other MDS/MPN category. Among these three patients, two had predominance of MPN features on bone marrow assessment (atypical megakaryocytes, and/or mild reticulin fibrosis) and one had BM blast% >5. Next generation sequencing (NGS) was done at diagnosis or first referral using institutional or commercially available myeloid malignancy-specific gene panels (details in Supplementary Table 1 ). Distribution of continuous variables was statistically compared using nonparametric (Mann-Whitney or Kruskal-Wallis) tests, while nominal variables were compared using the Chi-Square test. Time to event analyses used the method of Kaplan-Meier for univariate comparisons. Significant (P < 0. 05) continuous variables were converted into categorical variables after derivation of cut-off points through a receiver operating curve (ROC) analysis and were chosen for multivariate analysis performed through the Cox proportional hazard regression model. Overall survival (OS) was computed from the date of diagnosis to date of death or last follow-up. Leukemia-free survival (LFS) was calculated from date of diagnosis to date of acute myeloid leukemia (AML) transformation or last follow-up; in other words, AML transformation replaced death as the uncensored variable in calculating LFS. Patients who underwent allogeneic hematopoietic stem cell transplantation were censored at the time of transplantation.
section_name: METHODS

section_content: Overall, 183 patients were included in the study: 158 MDS/MPN-RS-T and 25 MDS/MPN-U-RS. The median age of the MDS/MPN-RS-T cohort was 71 (range: 38-94) years; 83 (52%) males. At last median follow-up of 62 [95% confidence interval (CI) 45-80) Table 1. In univariate analysis, age ≥70 years (HR 2, 95% CI 1. 2-3. 7, P = 0. 005), hemoglobin ≤10 g/dL (HR 2. 4, 95% CI 1. 1-5. 3, P = 0. 03), and abnormal karyotype (HR 3. 7, 95% CI 1. 4-9. 5, P = 0. 008) independently predicted shorter survival. In multivariate analysis, hemoglobin ≤10 g/dL (HR 3. 12, 95% CI 1. 1-8. 5, P = 0. 03) and abnormal karyotype (HR 7. 3, 95% CI 1. 1-8. 5, P = 0. 001) retained prognostic significance (Table 2 ). Importantly, none of the molecular abnormalities (Fig. 1 ), including ASXL1 (P = 0. 7, Fig. 1A ), SF3B1 (P = 0. 4, Fig. 1B ) or JAK2 V617F (P = 0. 7, Fig. 1C ), platelet count (P = 0. 2) or BM blast% (P = 0. 6) predicted survival. SF3B1 VAF information was available in only 43 patients, and was also not prognostically relevant (P = 0. 3). However, when only frameshift and nonsense ASXL1 mutations were considered, they were able to predict an adverse OS (P = 0. 02) in a univariate analysis, but not in a multivariate model (P = 0. 1). The prognostic irrelevance of molecular abnormalities such as ASXL1 (P = 0. 9), SF3B1 (P = 0. 4), or JAK2 V617F (P = 0. 8) persisted even in MDS/MPN-RS-T patients with a normal karyotype (n = 61). An operational survival model using hemoglobin ≤10 g/dL (1 point) and abnormal karyotype (1 point) delineated patients into low [0 points, median OS 10. 5 years, 95% CI (3-11. 3)], intermediate [1 point, median OS 4. 8 years, 95% CI (3. 4-6. 3)] and high-risk (2 points, median OS 1. 4 years, 95% CI (0. 5-not reached)] survival categories (Fig. 2 ). Among the highrisk patients (n = 8), three carried chromosome 7 abnormalities (1 with monosomy 7), two had a complex monosomal karyotype and 1 patient each had ASXL1 and TP53 mutations at diagnosis, respectively. 

Comparison of the 158 patients with MDS/MPN-RS-T and the 25 patients with MDS/MPN-U-RS revealed a higher frequency of SF3B1 mutations (92% versus 40%, P = 0. 003, Fig. 3A ) and AML transformation rate (4% versus 0%, P = 0. 0003) in MDS/MPN-RS-T (Table 1 ). Overall (median, 6 versus 7. 3 years, P = 0. 3, Fig. 3B ) and leukemia-free (median not reached in either groups, P = 0. 4) survival between the two groups was similar. Frequency of thrombosis (overall n = 14, 7-arterial, 7-venous, 11-before diagnosis, 3-after diagnosis) was also similar in the two groups (18% versus 8%, P = 0. 3, Table 1 ). Combined analysis of both groups did not identify platelet count <450 × 10 9 /L (HR 1. 1, 95% CI 0. 3-4. 7, P = 0. 9), BM blast% ≥5 (HR 1. 2 95% CI 0. 3-4. 96, P = 0. 8) or PB blast % ≥1 (HR 2. 4, 95% CI 0. 94-6. 2, P = 0. 07) to be prognostically relevant for OS (could not assess for LFS due to limited events). Similar to MDS/MPN-RS-T, age ≥70 years (HR 2. 04, 95% CI 1. 3-3. 3, P = 0. 004), Hb ≤10 g/dL (HR 2. 2, 95% CI 1. 14-4. 1, P = 0. 02), and abnormal cytogenetics [except -Y, HR 2. 4, 95% CI 1. 12-5. 4, P = 0. 02] significantly predicted inferior OS. Additionally, in the MDS/ MPN-U-RS group (n = 25), platelet count (P = 0. 9), BM blast% (P = 0. 8) or PB blast% (P = 0. 2) remained prognostically irrelevant for OS prediction.
section_name: RESULTS

section_content: MDS/MPN-RS-T patients, previously classified under the provisional WHO category of RARS-T, have been reported to have a median OS around 6 years, and leukemic transformation rate of ~2% [13] [14] [15]. Previously, hemoglobin <10 gm/dL, abnormal karyotype, ASXL1, and SETBP1 mutations have been found to significantly predict adverse OS [13] ; however, these data were based on RARS-T patients, which were not subject to MDS/MPN-RS-T exclusionary criteria such as PB blast% ≥1, BM blast% ≥5 or cytogenetic abnormalities such as t(3;3) (q21. 2;q26. 2), inv(3) (q21. 23q26. 2) or isolated del(5q). Further, ASXL1 and SETBP1 mutations were not statistically significant in a multivariate model [13]. When we reclassified our patients as per the contemporary WHO definition of MDS/MPN-RS-T, only Hb ≤10 gm/dL and abnormal karyotype (without -Y) retained independent prognostic significance. Although the presence of any ASXL1 mutation was unable to predict an adverse OS in a univariate analysis; frameshift and nonsense ASXL1 mutations were able to do so, similar to previously published studies [13, 16]. Another study identified SF3B1 and JAK2V617F as independent predictors of favorable prognosis, however these could not be validated in our cohort [17]. These data highlight that the contemporary WHOdefined MDS/MPN-RS-T category is clinically and molecularly less heterogenous than RARS-T, and yet this classification has key limitations. An operational survival model relying on hemoglobin and can be considered for aggressive therapeutic strategies such as an allogeneic hematopoietic stem cell transplantation. However, such a risk-adapted management approach would need prospective validation. 

The contemporary MDS/MPN-RS-T definition excludes patients with MDS/MPN-U with BM RS ≥ 15% if the platelet count is less than 450 × 10 9 /L, PB blast ≥1% or BM blast% ≥5. In our study, when we combined MDS/MPN-RS-T patients with MDS/MPN-U-RS, the platelet count, PB blast% or BM blast% did not predict for OS or LFS. Relevant clinical parameters such as frequency of thrombosis also did not significantly differ between the two groups. The prognostic irrelevance of platelet count, PB blast% or BM blast% remained true when MDS/MPN-U-RS cohort was separately analyzed. Application of these parameters as exclusion criteria for MDS/MPN-RS-T is therefore too restrictive and leaves out certain patients with MDS/MPN-U-RS, who have identical outcomes to MDS/MPN-RS-T patients as per the current definition. Limitations of the study include retrospective nature, heterogenous clinical and genomic information in the two institutional cohorts, and limited sample size. In conclusion, the findings from the current study did not identify molecular abnormalities as predictors of survival in MDS/MPN-RS-T, and also argue against the use of currently applied exclusionary criteria in defining MDS/MPN-RS-T, separate from MDS/MPN-U-RS. In other words, our observations support unification of MDS/MPN-U-RS and MDS/MPN-RS-T under a new category of "MDS/MPN-RS", pending independent external validation. This will allow uniform inclusion of MDS/MPN patients with RS in future clinical trials with novel drugs focused on reversing erythroid arrest such as TGFβ modulators, splicing inhibitors among others [18] [19] [20].
section_name: DISCUSSION

section_name: ACKNOWLEDGEMENTS

section_content: This publication was supported by Grant# UL1 from the National Center for Advancing Translational Sciences (NCATS), however findings do not necessarily represent official views of NIH.
section_name: ACKNOWLEDGEMENTS

section_name: AUTHOR CONTRIBUTIONS

section_content: AM compiled the clinical and genetic data, performed data analysis, and wrote the manuscript. TL performed NGS studies on some patients. RPK and KKR reviewed the pathology information. NG, AA, KHB, AP, NHA, CT, DS, EP, RK, AT, and MP contributed patients and edited all drafts of the manuscript. AM, AT, and MP conceptualized the study and edited all manuscript drafts. All authors contributed in the writing of the manuscript.
section_name: AUTHOR CONTRIBUTIONS

section_content: EP has received honoraria and/or serves on advisory boards of BluePrint, CTI, Stemline Therapeutics, Taiho, and BMS; and has received research funding from Kura, Incyte, and BMS. MP is on the advisory board of Stemline Therapeutics. All other authors declare no relevant conflicts of interest in relation to the manuscript.
section_name: COMPETING INTERESTS

section_content: The online version contains supplementary material available at https://doi. org/10. 1038/s41408-022-00622-8. 

Correspondence and requests for materials should be addressed to Abhishek A. Mangaonkar, Ayalew Tefferi or Rami Komrokji. 

Reprints and permission information is available at http://www. nature. com/ reprints Publisher's note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
section_name: ADDITIONAL INFORMATION Supplementary information