Of the most common spliceosome gene mutations (overall frequency > 0.5%), mutations in SF3B1 were more common in ER-positive breast cancer (2.2%, 21/936 ER-positive versus 0.3%, 1/289 ER-negative, p = 0.03914, Fisher's exact test) and mutations in SAP130 were more common in ER-negative tumours (0.1%, 1/936 ER-positive versus 1.4%, 4/289 ER-negative, p = 0.012, Fisher's exact test). This evidence concerns the gene SF3B1 and neoplasm.