ESR1 and breast carcinoma: Although this current study did not directly investigate ERα’s role, the overexpression of HIF-1α observed in both ERα + (Hc7 and Ac1-ExR) and ERα- (LTLTCa) HER2+ breast cancer cell lines, suggests that ERα status may not affect HER2 regulation of non-hypoxic HIF-1α levels.