PGR and breast cancer: Triple negative breast cancer (TNBC) lacksthe receptor biomarkersfound in other subtypes, making treatment challenging.1 Unlike hormone receptor (HR)-positive, human epidermalgrowth factor receptor 2 (HER2)-positive, estrogen receptor (ER),and progesterone receptor (PR) breast cancers, TBNC does not respondto targeted therapies,2,3 leaving chemotherapy as the primaryoption.4,5