bioRxiv2020
BackgroundSF3B1 mutations (SF3B1mut) in myelodysplastic syndromes (MDS) frequently involve codon K700E and have a favorable prognosis. The prognostic effect of non-K700E SF3B1mut is uncertain. MethodsWe analyzed the clinical-pathologic features and outcomes of a single-institutional series of 94 SF3B1mut and 415 SF3B1wt newly diagnosed untreated MDS patients and explored the differences between K700E and non-K700E subgroups. FindingsNinety-four (19%) patients had SF3B1mut: median age, 74 years. Fifty-five (60%) patients carried K700E. Recurrent non-K700E mutations (39, 40%) included R625, H662 and K666. Compared to SF3B1mut K700E, non-K700E patients had a lower median ANC (1{middle dot}8 vs. 2{middle dot}4, p=0{middle dot}005) and were frequently "high" R-IPSS (revised International Prognostic Scoring System) [7(19%) vs. 2(4%), p=0{middle dot}031]. Non-K700E MDS frequently associated with RUNX1 (26% vs. 7%, p=0{middle dot}012) and exclusively with BCOR, IDH2, and SRSF2 mutations. There was no significant difference in karyotype or SF3B1 variant allele frequency. Most ([~]80%) were treated with hypomethylating agents. SF3B1mut had superior overall survival (OS) than SF3B1wt in all MDS categories [not-reached vs. 25{middle dot}2 months, p=0{middle dot}0003], low-grade MDS, and MDS with ring sideroblasts (MDS-RS). Compared to SF3B1wt, SF3B1mut K700E had superior outcomes in all MDS categories (25 months vs. not-reached, p=0{middle dot}0001), low-grade MDS, and MDS-RS, but no significant difference was seen with non-K700E. By multivariate analysis, absence of SF3B1mut K700E (not non-K700E) independently associated with prognosis. InterpretationSF3B1mut MDS show distinct clinical and mutational profiles, with K700E showing a significantly better OS compared to non-K700E mutations and SF3B1wt. Our study highlights the importance of SF3B1 mutation type in MDS risk assessment. Data Sharing StatementThe datasets generated during and/or analyzed during the current study are not publicly available due to patient privacy concerns but are available from the corresponding author on reasonable request. Research in ContextO_ST_ABSEvidence before this studyC_ST_ABSWe designed this study based on the collective evidence from a systematic search of the literature for outcomes of patients MDS with SF3B1 mutations (SF3B1mut) from January 2013 to June 2020. Both the International Working Group for the Prognosis of MDS (IWG-PM) proposal and 2016 revisions to the World Health Organization (WHO) Classification of Myelodysplastic Syndromes recognize SF3B1mut MDS with <5% blasts (or ring sideroblasts >5% for WHO) as a distinct sub-category, in the absence of other unfavorable features. This was largely based on favorable prognostic outcomes, a distinct gene expression profile, and association with ring sideroblasts. However, the natural history of SF3B1mut MDS is heterogeneous. A high proportion of SF3B1 mutations occur within codon K700, leading to large-scale mRNA downregulation due to branch point recognition error, while the rest occur outside of this codon. The downstream functional effects of SF3B1 mutations outside of the K700 codon are unclear. The clinical course of SF3B1mut MDS patients likely depends on the type of SF3B1 mutation and other features such as variant allele frequency, concomitant gene mutations, and karyotype. Until now, the effects of the different types of SF3B1 mutations were largely unknown. Added value of this studyIn this study, we report distinctive clinicopathologic characteristics and outcomes of MDS patients with SF3B1 mutations segregated based on mutation type: K700E vs. non-K700E. We show that [~]40% of SF3B1 mutated MDS patients have non-K700E mutations. Non-K700E SF3B1mut MDS have distinct clinico-pathologic features, such as lower ANC and frequent association with mutations in RUNX1, BCOR, IDH2, and SRSF2. There was no significant difference in karyotype or SF3B1 variant allele frequency. Importantly, K700E SF3B1mut MDS had superior overall survival compared to SF3B1wt, in all MDS, low-grade MDS, and MDS with ring sideroblasts, but no significant difference was seen with non-K700E. By multivariate analysis, absence of SF3B1mut K700E, but not non-K700E, independently associated with prognosis. Implications of all the available evidenceTo the best of our knowledge, this is the first study to report these findings from a single-institutional series of MDS primarily treated with hypomethylating agents. Our study highlights the importance of determining the SF3B1 mutation type in MDS risk assessment. These findings are important in light of the recent FDA approval of luspatercept based on the results of the MEDALIST trial that suggested sustained hematological responses in SF3B1mut MDS patients.