PGR and cancer: Breast cancer is the leading cause of cancer-related death in women.1–3 Currently, the most classic molecular targets for breast cancers include human epidermal growth factor receptor 2 (HER-2/neu), oestrogen receptor (ER), and progesterone receptor (PR).4–7 However, due to the heterogeneous molecular alterations in the breast cancer cells, patients with highly aggressive triple-negative breast cancer (TNBC) cannot benefit from HER-2/ER/PR-targeted therapies.8,9 The development of new targeting strategies, particularly for TNBCs, is urgently needed.