Several genomic studies in breast cancer have revealed that MAP3K1 alterations are most common in the luminal A subtype of breast cancer.13–16 The pattern of mutations observed both in our study (Supplementary Fig. 1) and in large-scale genomic efforts16 suggest loss-of-function, due to the predominance of truncating and frameshift alterations. Here, MAP3K1 is linked to breast carcinoma.