To confirm the cytotoxic effect of a combination of paclitaxel and XAV939 on TNBC cell lines (MDA-MB-231, MDA-MB-468, BT549) and ER+ve cells (MCF-7, T-47D), each cancer cell line was treated with paclitaxel (20 nM, 40 nM, and 200 nM), XAV939 (5 μM and 10 μM), and paclitaxel + XAV939 (20 nM + 5 μM, 20 nM + 10 μM, 40 nM + 5μM, and 40 nM + 10 μM), for 24 h, 48 h, and 72 h. The gene discussed is ESR1; the disease is cancer.