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. This evidence concerns the gene ESR1 and breast cancer.