SF3B1 and breast carcinoma: Overall, mutations in SF3B1 were the most common spliceosomal component gene mutation and were identified in 1.8% of unselected breast cancers (23/1293), and occurred as a recurrent hotspot T > C base-pair substitution at codon 700, leading to a glutamic acid from lysine (K700E) in 74% (17/23) of mutant cases (Figure 1B and Table 1).