SF3B1 (splicing factor 3b subunit 1), which aids in the recognition of consensus sequences in introns to promote efficient mRNA splicing, is the most frequently mutated splicing factor in cancer, with particular enrichment in various haematological malignancies—including acute myeloid leukaemia [3], myelodysplastic syndromes and chronic lymphocytic leukaemia [4], as well as uveal melanomas [5, 6] and other solid tumours such as skin [7] and breast cancers [8]. The gene discussed is SF3B1; the disease is breast cancer.