PIK3CA and breast neoplasm: HER2-low breast tumors also had significantly higher mutations rates in CBFB (p < 0.05), PIK3CA (p < 0.05), mitogen-activated protein kinase kinase kinase 1 (MAP3K1; p < 0.05), and AT-rich interaction domain 1A (ARID1A; p < 0.05) as compared with HER2-zero breast tumors (Fig. 3C, Additional file 1: Fig. S2C).