Triple-negative breast cancer (TNBC), characterized by the absence of human epidermal growth factor receptor 2 (HER2) overexpression as well as estrogen receptor (ER) and progesterone receptor (PR) negativity [1–3], accounts for approximately 10% of incident breast cancers and has the poorest prognosis among breast cancer subtypes [1–3]. This evidence concerns the gene PGR and breast cancer.