PGR and breast cancer: Notably, gene expression profiling has revealed that MMTV-PyMT tumors cluster closely with ERα-negative “luminal” human breast cancers [68], which is a gene signature similar to the luminal-AR (LAR) TNBC subtype characterized by high AR expression [69] and the molecular apocrine ER/PR-negative, but AR+ tumors described prior to molecular subtyping [70].