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Background SF3B1 mutations (SF3B1mut) in myelodysplastic syndromes (MDS) frequently involve codon K700E and have a favorable prognosis. The prognostic effect of non‐K700E SF3B1mut is uncertain. Methods The authors analyzed the clinicopathological features and outcomes of a single‐institution series of 94 treatment‐naive SF3B1mut MDS patients (18%) and 415 treatment‐naive SF3B1wt MDS patients and explored the differences between K700E and non‐K700E SF3B1mut MDS. Results Fifty‐five patients (59%) carried K700E. Recurrent non‐K700E mutations (39 [41%]) included R625, H662, and K666. Compared with SF3B1mut K700E patients, non‐K700E patients had a lower median absolute neutrophil count (1.8 vs 2.4; P = .005) and were frequently “high” according to the Revised International Prognostic Scoring System (19% vs 4%; P = .031). Non‐K700E MDS was associated frequently with RUNX1 (26% vs 7%; P = .012) and exclusively with BCOR, IDH2, and SRSF2 mutations. A splicing analysis showed the differential distribution of alternatively spliced events and gene expression profiles between K700 and non‐K700E MDS patients. The majority (at least 80%) of SF3B1mut K700E, SF3B1mut non‐K700E, and SF3B1wt patients were treated with hypomethylating agents. Over a median follow‐up of 16 months, SF3B1mut had superior overall survival (OS) in comparison with SF3B1wt in all MDS patients (not reached vs 25.2 months; P = .0003), in patients with low‐grade MDS, and in patients with myelodysplastic syndromes with ring sideroblasts (MDS‐RS). Compared with SF3B1wt, SF3B1mut K700E had superior outcomes in all MDS (median OS, 25 months vs not reached; P = .0001), in low‐grade MDS (median OS, 41.3 months vs not reached; P = .0015), and in MDS‐RS (median OS, 22.3 months vs not reached; P = .0001), but no significant difference was seen between non‐K700E and SF3B1wt MDS. By multivariable analysis, the absence of SF3B1mut K700E mutations was independently associated with the prognosis. Conclusions This study highlights the importance of the SF3B1 mutation subtype in MDS risk assessment. Lay Summary Myelodysplastic syndromes (MDS) with SF3B1 mutations are regarded as having a favorable prognosis by both the World Health Organization and the International Working Group for the Prognosis of Myelodysplastic Syndromes. However, this article shows that only MDS patients with SF3B1 K700E mutations have a favorable prognosis (and not MDS patients with SF3B1 mutations involving other codons). This has important implications for refining future MDS subclassification and risk assessment criteria.

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Classification of myeloid neoplasms with isolated i(17q) [17p deletion with inherent monoallelic TP53 loss plus 17q duplication] is controversial. Most cases fall within the WHO unclassifiable myelodysplastic/myeloproliferative neoplasms (MDS/MPN-U) category. The uniformly dismal outcomes warrant better understanding of this entity. We undertook a multi-institutional retrospective study of 92 adult MDS/MPN-U cases from eight institutions. Twenty-nine (32%) patients had isolated i(17q) [MDS/MPN-i(17q)]. Compared to MDS/MPN without i(17q), MDS/MPN-i(17q) patients were significantly younger, had lower platelet and absolute neutrophil counts, and higher frequency of splenomegaly and circulating blasts. MDS/MPN-i(17q) cases showed frequent bilobed neutrophils (75% vs. 23%; P = 0.03), hypolobated megakaryocytes (62% vs. 20%; P = 0.06), and a higher frequency of SETBP1 (69% vs. 5%; P = 0.002) and SRSF2 (63% vs. 5%; P = 0.006) mutations which were frequently co-existent (44% vs. 0%; P = 0.01). TP53 mutations were rare. The mutation profile of MDS/MPN-U-i(17q) was similar to other myeloid neoplasms with i(17q) including atypical chronic myeloid leukemia, chronic myelomonocytic leukemia, myelodysplastic/myeloproliferative neoplasm with ring sideroblasts and thrombocytosis, myelodysplastic syndrome and acute myeloid leukemia, with frequent concomitant SETBP1/SRSF2 mutations observed across all the diagnostic entities. Over a median follow-up of 52 months, patients with MDS/MPN-i(17q) showed a shorter median overall survival (11 vs. 28 months; P < 0.001). The presence of i(17q) retained independent poor prognostic value in multivariable Cox-regression analysis [HR 3.686 (1.17 – 11.6); P = 0.026] along with splenomegaly. We suggest that MDS/MPN-i(17q) warrants recognition as a distinct subtype within the MDS/MPN-U category based on its unique clinico-biologic features and uniformly poor prognosis.