PGR and breast cancer: American women of African ancestry (AA) are more likely to develop breast cancer at a younger age than those with European ancestry (EA) and are more likely to have tumors with aggressive characteristics, including high histological grade, negative estrogen receptor (ER) status, and basal-like - ER- and/or progesterone receptor (PR)-, HER2-, and cytokeratin 5/6+ and/or HER1+ -features [1,2].