Progesterone did not alter BRCA1/2 expression but markedly suppressed the expression of PARP1/2/3, TOPO-I, TIMELESS, and TIPIN.<h4>Conclusions</h4>Progesterone enhances the sensitivity of ovarian cancer cells to PARP inhibitors by downregulating TRC-protective factors via mPR-mediated non-genomic actions. The gene discussed is BRCA1; the disease is ovarian cancer.