PIK3CA mutations, which are particularly enriched in estrogen receptor (ER)-positive and luminal subtype cancers (Supplementary Fig. 15a, b), showed a tendency to be mutually exclusive with mutations in TP53 (Supplementary Fig. 15c; P < 0.0001, Fisher’s exact test), which occur more frequently in basal-like tumours. Here, ESR1 is linked to cancer.