PIK3CA and breast cancer: Endocrine-sensitive and LTED BC cell lines retaining ER expression and with varying levels of EGFR, ERBB2, ERBB3, and FRAP1 expression [21] and differing PIK3CA, ERBB2, and ESR1 mutation status (Additional file 1: Figure S1a, b) were assessed for their sensitivity to escalating doses of RAD001 (Fig. 2a) or neratinib (Fig. 2b) in the presence or absence of E2.