Working independently some years later, Xia and colleagues42 reported in vitro experiments in HR+/HER2-overexpressing breast cancer cell lines and tumor xenograft models confirming the rationale for dual ER/HER2 blockade, this time with lapatinib plus fulvestrant to enhance efficacy (vs. monotherapy with either agent alone as controls), using a different HER2-targeting agent and different model systems, yet completely consistent with the earlier findings published by Pietras36. This evidence concerns the gene ESR1 and breast cancer.