PIK3CA and breast cancer: We first examined the effect of Melatonin on cell survival in three HER2+ breast cancer cell lines that carry oncogenic PIK3CA mutations, including HCC1954 (HER2 amplification, PIK3CA H1047R) and MDA-MB-361 (HER2 amplification, PIK3CA E545K), and MCF7 (PIK3CA E545K) with ectopic overexpression of HER2 (MCF7/HER2).