As highlighted previously, our aim was to demonstrate the in vitro effects of V9302 on different subtypes of breast cancers, namely estrogen, progesterone, and HER2 receptor-negative ATCC HTB-26TM (MDA-MB-231), estrogen receptor-positive, Pgp-overexpressing KCR, estrogen receptor-, and progesterone receptor-positive MCF-7 (ATCC HTB22 the parental non-resistant cell line of KCR), and estrogen receptor-positive T-47D (HTB-133TM). This evidence concerns the gene ESR1 and breast cancer.