Treatment of MCF-7 and triple-negative MDA-MB-231 breast cancer cells with cytotoxic agent doxorubicin (10-9 M; positive control) or with the GnRH-II antagonist (10-9 and 10-7 M) for 72 h resulted in a reduction of mitochondrial membrane potential. The gene discussed is GNRH2; the disease is breast carcinoma.