PGR and breast cancer: Triple-negative breast cancer (estrogen receptor [ER]-negative, progesterone receptor [PgR]-negative, and human epidermal growth factor receptor 2 [HER2]-negative) accounts for approximately 12–17% of all breast cancers and is associated with poor outcomes, with an increase in the risk of recurrence compared to other breast cancer subtypes and more frequent spread to visceral organs and the central nervous system (CNS) [1–4].