PGRMC1 and breast cancer: In breast cancer, progestins initiate a non-classical signaling of membrane progesterone receptors (mPRs) and progesterone receptor membrane component 1 (PGRMC1) by activating downstream targets, protein kinase c (PKC), protein kinase a (PKA), cyclic guanosine monophosphate (cGMP), and AKT, leading to Ca2+ influx, proliferation, and cell survival [42] (Figure 1A).