PGR and breast cancer: Taken together, these results demonstrate that PGRMC1-overexpression sensitizes ERα/PR positive luminal breast cancer cells to treatment with specific progestins (NET, DYD, DSP, and MPA; proliferation-promoting progestins, hereafter referred to as PPPs), while other progestins (CPA, NOM and P4; non-proliferation-promoting progestins, hereafter referred to as N-PPPs) did not enhance proliferation under any condition.