ESR1 and breast cancer: Sensitivity to neratinib, dasatinib, and the combination was first assessed in 16 breast cancer cell lines representing the three main clinical subtypes: eight HER2+ breast cancer cell lines (including models of innate and acquired trastuzumab-resistance), six triple negative breast cancer (TNBC) cell lines, and two estrogen receptor-positive (ER+) breast cancer models (Table 1).