U2AF1 and essential thrombocythemia: In addition, a previous study demonstrated that 15% of ET patients harbor one or more non-driver mutations in SRSF2, U2AF1, SF3B1 or TP53; moreover, the presence of mutations in SRSF2 and SF3B1, SF3B1 and U2AF1, or in TP53 was associated with significantly lower rates of overall, myelofibrosis-free, and leukemia-free survival, respectively [101].