PIK3CA and breast cancer: Known genetic drivers of breast cancer were detected in biopsies of 5 patients, including TP53 mutations in samples from 5 of 6 patients, hotspot mutations in FGFR1 (n = 1), ERBB2 (n = 1) and PIK3CA (n = 1), and mutations in TBX3 (n = 2) and MAP3K1 (n = 3; Fig. 3B).