SRSF2 is Mutated in 47.2% (77/163) of Chronic Myelomonocytic Leukemia (CMML) and Prognostically Favorable in Cases with Concomitant RUNX1 mutations

Chronic myelomonocytic leukemia (CMML) is a clonal hematopoietic malignancy characterized by features of both a myeloproliferative neoplasm and a myelodysplastic syndrome. We previously investigated 81 CMML cases and detected a number of genes frequently mutated (TET2 44.4%, CBL 22.2%, NRAS 22.2%, KRAS 12.3%, JAK2 9.8%, RUNX1 8.7%, EZH2 12.3% (Kohlmann et al., JCO, 2010; Grossmann et al., Leukemia, 2011). Recently, we detected a new candidate gene, SRSF2 (serine/arginine-rich splicing factor 2, also known as SC35) that is a component of the RNA splicing machinery and found it to be frequently mutated in MDS. Aim: As CMML has been increasingly characterized by a growing number of genes during the last years we here analyzed both the frequency of SRSF2 mutations in this entity and the relevance in the context of other previously described gene mutations, as well as to look for a potential prognostic implication. Patients and Methods: In total, 163 cases with CMML (CMML-1 n=105, CMML-2 n=58) were included. The cohort comprised 115 males and 48 females with a median age of 72.8 yrs (range: 21.9 – 88.8 yrs) including all 81 pts that have been published previously. 112 cases (69%) had a normal karyotype and 51 (31%) showed aberrant karyotypes. The mutational hot spot region of SRSF2 around Proline codon 95 (P95) was analyzed by Sanger sequencing in all cases. Data on further mutations were available in respective subcohorts: ASXL1 (n=128), CBL (n=162), EZH2 (n=134), JAK2V617F (n=162), KRAS (n=140), NRAS (n=79), RUNX1 (n=156), TET2 (n=143), TP53 (n=80). Results:SRSF2 mutations of P95 were detected in 77/163 (47.2%) of all cases (49/105, 46.7% in CMML-1, and 28/58, 48.3% in CMML-2). In detail, 74 cases had a missense mutation leading to a change of P95 to P95H (n=33), P95L (n=24), P95R (n=16) or P95A (n=1). In further 3 cases a newly described 24 bp (8 amino acids) deletion starting at P95 was observed. All cases had a mutation load of approximately 50%. The mutations were correlated with higher age (73.3 yrs vs 68.7 yrs in the SRSF2wt cases, p=0.010) and higher hemoglobin levels (11.4 vs 10.5 g/dl in the SRSF2wt cases, p=0.019) whereas white blood cell counts were not different. Further, SRSF2 mutations were mutually exclusive of EZH2 mutations (0/12, 0% vs. 66/122, 54.1% in the EZH2wt, p<0.001) whereas a high coincidence occurred with RUNX1 mutations (22/35, 62.9% vs 52/121, 43% in the RUNX1wt, p=0.054) and TET2 mutations (50/82, 61% vs 18/61, 29.5% in the TET2wt, p<0.001). With respect to associations with all other gene mutations investigated and karyotype no specific pattern was observed. In the total cohort no impact of SRSF2 on survival was observed. Because of the high coincidence of SRSF2mut with RUNX1mut and TET2mut, we performed an analysis in these specific subcohorts. No impact of SRSF2mut in the TET2mut subcohort was found. Whereas in the RUNX1mut subcohort SRSF2mut had a favorable impact on overall survival compared to SRSF2wt (median OS: 108.0 months vs 41.8 months, p=0.05). Conclusions:SRSF2 has recently been described as a new marker in CMML and demonstrated to be useful to delineate further the genetic defects of this disease. This very frequent new mutation is characterized by higher age, higher hemoglobin levels and a high coincidence with TET2 and RUNX1 mutations. It is mutually exclusive of EZH2 mutations. In the subset of RUNX1 mutated CMML SRSF2 mutations demonstrated a favorable impact on outcome. Furthermore, for the first time a 24 bp deletion was observed in three cases that may provide further insight into the structural basis for the abnormal function of SRSF2.

Schnittger:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Meggendorfer:MLL Munich Leukemia Laboratory: Employment. Kohlmann:MLL Munich Leukemia Laboratory: Employment. Grossmann:MLL Munich Leukemia Laboratory: Employment. Kern:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership.