PGR and breast cancer: To analyze the effects of GnRH-II antagonist treatment on induction of apoptosis in estrogen receptor/progesterone receptor-positive MCF-7 human breast cancer cells, which have a normal expression of HER1-neu and triple-negative MDA-MB-231 human breast cancer cells, GnRH-II antagonist-induced loss of mitochondrial membrane potential (ΔΨ) was measured (Figure 1a).