U2AF1 and hematopoietic and lymphoid cell neoplasm: The U2AF1 gene encodes a core component of the mRNA splicing machinery that is frequently mutated in myelodysplastic syndrome (MDS) and other cancers.1, 2, 3 Though predominantly associated with hematopoietic cancers (73%), mutations are also recurrent in lung tumors (6.5%) and have been reported in 24 other tumor types.