Validation of the 2016 revisions to the <scp>WHO</scp> classification in lower‐risk myelodysplastic syndrome
Authors: Rashmi Kanagal‐Shamanna, Juliana E. Hidalgo Lopez, Denái R. Milton, Hye Ryoun Kim, Chong Zhao, Zhuang Zuo, Michelle Janania Martinez, Francesco Stingo, John Lee, Rajyalakshmi Luthra, Elias J. Jabbour, Guillermo Garcia‐Manero, L. Jeffrey Medeiros, Carlos E. Bueso‐Ramos
Journal: American Journal of Hematology (2017)

"Lower-risk" (LR) myelodysplastic syndrome (MDS) is defined as low and intermediate-1 risk by International Prognostic Scoring System (IPSS). Currently available prognostic models lack the ability to identify LR-MDS patients with poor outcome who may benefit from early therapy.1 These models, unlike WHO-based systems, do not incorporate morphologic parameters such as lineage dysplasia and percentage (%) of ring sideroblasts (RS). The recent 2016 World Health Organization (WHO) revisions for MDS classification attempts to create biologically homogeneous subgroups by refining morphologic criteria and incorporating genetic information. These include emphasis on the number of dysplastic lineage(s), accurate enumeration of blasts and RS and assessment of SF3B1 mutation in MDS with ≥5% RS. The most important change includes addition of MDS-RS with multilineage dysplasia (MDS-RS-MLD) category for patients with either "RS ≥ 15%" or "RS ≥ 5% and SF3B1 mutation". All the proposed changes are within MDS categories with <5% blasts that mostly belong to LR IPSS.2 In this study, we assessed the prognostic value of the revised 2016 WHO system in a series of MDS patients with <5% blasts and diploid karyotype. The WHO systems do not use karyotype to define subtypes other than del(5q). However, the karyotype is highly prognostic in MDS and can independently affect outcome; further, the prognostic effect of different cytogenetic abnormalities varies.1 In order to assess the prognostic value of MDS categories in the revised 2016 WHO system and eliminate the confounding effects of various karyotypes, we applied this system in a uniform cohort composed of consecutive MDS patients with <5% blasts with diploid karyotype by conventional cytogenetic analysis. The study group included 218 consecutive diploid karyotype MDS patients with <5% blasts presenting to our institution (2005-2010). Based on these criteria, all patients were LR-IPSS. All patients had clinical, laboratory and bone marrow (BM) evaluation at the time of initial diagnosis prior to receiving any therapy. Although patients presented at various time points of disease evolution, cases were sub-classified using IPSS and R-IPSS risk-stratification, as well as 2008/2016 WHO criteria based on the parameters at the time of diagnosis prior to receiving treatment. BM findings, both at the time of initial diagnosis (pre-treatment) and at the time of presentation to our institution, were reviewed on all patients independently by two hematopathologists (R.K-S, C.B-R) using standard criteria. SF3B1 mutation analysis was done using PCR-based Sanger sequencing for (exons 14 and 15). The detailed methods are described in Supporting Information File 1. The clinicopathologic characteristics, IPSS and R-IPSS risk stratification, and distribution by 2008/2016 WHO classification categories are presented in Figure 1. Using 2016 WHO criteria, 59 of 188 (31%) refractory cytopenia with multilineage dysplasia (RCMD) patients were reclassified as "MDS-RS-MLD" [57 with RS > 15%; 2 with RS > 5% and SF3B1 mutation]. The proportion of cases reclassified as MDS-RS-MLD was comparable to Strupp et al. (24.4%) that included MDS with various abnormal karyotypes,3 and much lower than Li et al. (59%) that only selected for MDS with >1% RS.4 A: Patient characteristics and distribution of cases by IPSS and R-IPSS risk stratification and 2008 and 2016 WHO classification systems. B,C: Leukemia-free survival (LFS) outcome of lower-risk myelodysplastic syndrome (MDS) patients with diploid karyotype; Kaplan-Meier survival curves representing (B) LFS in subgroups categorized using 2016 WHO system; (C) LFS in subgroups categorized using R-IPSS (very low, low, intermediate, and high-risk); and (D) LFS in subgroups categorized as MDS-RS-MLD and MDS-MLD using 2016 WHO system in patients who never received treatment with disease modifying drugs during the entire course of the disease until the end of the study period. MDS-MLD, MDS with multilineage dysplasia; MDS-RS-MLD, MDS with ring sideroblasts with multilineage dysplasia; MDS-SLD, MDS with single lineage dysplasia; MDS-RS-SLD, MDS with ring sideroblasts with single lineage dysplasia; RARS, Refractory Anemia with Ring sideroblasts; RCUD, Refractory Anemia with Unilineage Dysplasia; RCMD, Refractory Anemia with Multilineage Dysplasia; R-IPSS, Revised International Prognostic Scoring System; WHO, World Health Organization. [Color figure can be viewed at wileyonlinelibrary.com] The median follow-up interval was 30.7 months (range: <1-185.3); 86 (40%) patients died. The median OS and LFS were 75.3 and 70.0 months, respectively. The median OS and LFS for patient groups classified by IPSS/R-IPSS/2008/2016 WHO are provided in Supporting Information File 2. By univariate analysis, lower age (OS, P = .002; LFS, P = .004), higher hemoglobin level (OS/LFS, P < .001) and presence of absolute neutropenia (OS, P = .041; LFS, P = .047) were associated with better OS/LFS. Within R-IPSS, "very-low" risk patients had significantly better OS/LFS compared with "intermediate" risk patients (OS, P = .011; LFS, P = .008). Within 2016 WHO, MDS-RS-MLD patients had significantly better OS/LFS compared with MDS-MLD patients (OS, P = .042; LFS, P = .037). There was no significant difference in outcome between IPSS or 2008 WHO categories. About 85 of 218 (39%) patients received only supportive therapy (no disease modifying drugs) during the entire disease course. Within this subgroup, MDS-RS-MLD patients had significantly better OS compared with MDS-MLD (not-reached versus 36.8 months, P = .013). MDS patients with RS ≥ 15% with single/multilineage dysplasia ("MDS-RS-MLD" or "MDS-RS-SLD") had significantly better OS compared with MDS without RS ≥ 15% ("MDS-SLD" or "MDS-MLD") [not-reached versus 46.7 months, P = .014]. In contrast, MDS patients with multilineage dysplasia irrespective of RS% ("MDS-RS-MLD" or "MDS-MLD") had no significant difference in OS compared with MDS showing single lineage dysplasia ("MDS-RS-SLD" or "MDS-SLD") [not-reached in both]. This suggests that RS > 15% has more prognostic value than the number of dysplastic lineage(s). No significant differences in OS were observed between R-IPSS categories [very-low risk, not-reached; low-risk, 57.5 months; intermediate-risk, not-reached]. Using multivariable models for OS and LFS that included both 2016 WHO and R-IPSS, classification by 2016 WHO classification approached significance [OS, P = .06; LFS, P = .07]. Within 2016 WHO, MDS-RS-MLD patients had significantly better OS (P = .016) and LFS (P = .015) compared with MDS-MLD. Other independent adverse prognostic factors included lower hemoglobin (P = .002) and absence of absolute neutropenia (P = .013). R-IPSS was not independently associated with OS or LFS (Supporting Information File 3). Sixteen patients had AML transformation; the median time-to-transformation was not reached (5-year rate 11%; overall-rate 30%). Eighty patients underwent SF3B1 analysis [35 with RS < 5%; 19 with 5%-14% RS; 26 with RS ≥ 15%]; 15 (18.8%) patients had SF3B1mut [3% in RS < 5%; 11% RS 5%-14%; 48% in RS ≥ 15%]. SF3B1mut MDS patients were more frequently classified as IPSS low-risk (80% versus 51%, P = .0472) and MDS-RS-MLD by 2016 WHO (87% vs. 22%, P = .0001), and less frequently as MDS-MLD (6% vs. 74%, P = .0001) compared with SF3B1mut. There were no significant differences between the two groups in the distribution of R-IPSS categories. SF3B1mut MDS patients had a longer OS compared with patients with SF3B1wt MDS (not-reached vs. 67.3 months); the difference was not significant, possibly due to small number. The category of "RCMD-RS," based solely on >15% RS, created in the 2001 WHO classification, was eliminated from the 2008 WHO. Following identification of SF3B1 mutation, the distinctive phenotype with increased RS [refractory anemia with ring sideroblasts (RARS) and RCMD-RS] and the favorable outcome of SF3B1mut MDS, irrespective of RS% or multilineage dysplasia were recognized. RARS and RCMD-RS also shared similar gene expression profiles that were distinct from other entities. Hence, the 2016 WHO revision proposed separate categorization of MDS-RS-MLD.2 In this study, MDS-RS-MLD patients had a significantly better OS and LFS compared with MDS-MLD by multivariate analysis. Our findings strongly support the 2016 WHO revision. Our study group was homogeneous with respect to karyotype. In another study that included MDS patients with various abnormal karyotypes that might have independently affected outcome, no significant difference in OS or AML progression was noted between these categories.3 The overall frequency of SF3B1mut in this cohort is slightly lower compared with others.5 Our study group was smaller as it focused only on MDS with diploid karyotype. SF3B1mut was analyzed using Sanger sequencing of exons 14 and 15 (sensitivity 10%-20%); hence, subclonal mutations (described in up to 22% of MDS patients) and mutations outside of the tested exons are missed.5, 6 Nevertheless, the low frequency of SF3B1mut in MDS with RS < 5% supports the 2016 WHO recommendation of 5%-14% RS to trigger mutation testing. In conclusion, 2016 revised WHO classification provides additional prognostic information, and should be used in conjunction with other available models for MDS management. The findings emphasize the value of recognizing multilineage dysplasia, accurate enumeration of RS, and SF3B1 mutation in MDS for accurate sub-categorization, prognostication and potential use of splicing factor therapy. This work was in part supported by institutional start-up funds awarded to RK-S and in part by the Cancer Center Support Grant (NCI Grant P30 CA016672). The authors declare no competing financial interests. Additional Supporting Information may be found online in the supporting information tab for this article. Supporting Information File 1 (Methods) Supporting Information File 2 (Table). Overall survival and leukemia-free survival in MDS patients with diploid karyotype classified using IPSS, R-IPSS, 2008 WHO and 2016 WHO systems Supporting Information File 3 (Table). Results of the multivariable models including 2016 WHO system and R-IPSS categories for overall and leukemia-free survival 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.