In this study, we assessed the effect of the combined therapy of the mTORC1 inhibitor, RAD001, with additional co-blockade of ERBB signalling with neratinib, an irreversible pan-ERBB receptor tyrosine kinase (RTK) inhibitor [11–13], in human BC cell models of endocrine-sensitive and -resistant disease with varying ESR1, PIK3CA, and ERBB2 mutation status. The gene discussed is ESR1; the disease is breast cancer.