U2AF1 and acute myeloid leukemia: Some AML cases are the results of transformation from previously diagnosed MDS, MPN, or MDS/MPN, and such patients with “secondary AML” have poorer prognosis than de novo AML (19) and often carry so-called “secondary-type” gene mutations in SRSF2, SF3B1, U2AF1, ZRSR2, ASXL1, EZH2, BCOR, or STAG2 (13).