PGR and breast cancer: However, compared to never users, ever SSRI users had significantly elevated risks of progesterone receptor (PR) negative and oestrogen receptor (ER) positive/PR-negative breast cancers (OR 1.8, 95% CI 1.1–3.6 and OR 2.0, 95% CI 1.1–3.8, respectively), but not of tumours with other hormone receptor profiles.