Conjugate 19 showed slightly higher cytotoxic activity against ER(+) breast cancer cells (MCF-7) than ER(−) ones (MDA-MB-231) and also higher than a non-tumoral fibroblast cell line (MRC-5), with IC50 values of 5.9 μM, 9.3 μM, and 9.1 μM respectively. The gene discussed is ESR1; the disease is breast cancer.