In a large cohort of 4079 Chinese women with breast cancer, the most common somatic mutations were TP53 (49.9%), PIK3CA (30.1%), GATA3 (10.0%), NF1 (6.0%), and MAP3K1 (5.4%), with TP53 and BRCA1 mutations enriched in TNBC. The gene discussed is PIK3CA; the disease is breast cancer.