PGR and breast cancer: Triple-negative breast cancer (TNBC), comprising 10–20% of all breast cancers, is a subgroup of breast cancer showing diverse and heterogeneous features with lack of estrogen receptor (ER) and progesterone receptor (PR) expression as well as human epidermal growth factor receptor 2 (HER2) amplification (2,3) and is inadequate to established hormonal therapy and/or HER2 targeted therapy due to the lack of these proteins (4).