In this preclinical study, we tested the cytotoxic effect of NG25 and its effects on Dox treatment on breast cancer cells by using a panel of breast cancer cell lines including T-47D, MCF7, HCC1954, MDA-MB-231, and BT-549 (representing ER/PR+, HER2+, or triple negative, respectively). The gene discussed is ESR1; the disease is breast carcinoma.