PGR and breast cancer: Triple‐negative breast cancer (TNBC), the most aggressive subtype of breast cancer, accounts for 15%–20% of all cases and is characterized by a high propensity for invasion, metastasis, and therapeutic resistance.[1] Defined by the absence of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), TNBC also exhibits marked intratumoral heterogeneity.[2] Although considerable progress has been made in delineating its molecular landscape, the contribution of environmental factors to TNBC progression remains poorly understood.