U2AF1 mutations rarely co-occur with other common splicing factor mutations (SRSF2, SF3B1, ZSZR2).40,41 In a cohort of 202 MDS/AML patients at Cleveland Clinic, only eight patients acquired comutations of U2AF1 and other splicing factors with variable variant allele frequency (VAF) in both hits (Fig.1B). This evidence concerns the gene SF3B1 and myelodysplastic syndrome.