RNA splicing factor SF3B1 is recurrently mutated in various cancer types, including chronic lymphocytic leukemia (CLL) (1–3), myeloid dysplasia (MDS) (4, 5), acute myeloid leukemia (6), uveal melanoma (UVM) (7), and breast and pancreatic cancers (8–10). Here, SF3B1 is linked to B-cell chronic lymphocytic leukemia.