PGR and breast cancer: [7, 10, 11, 13] We detected a very strong association between current (vs. never) smoking and ER+/PR- breast cancer (1.92; 1.19–3.10), followed by a weaker but robust association with ER+/PR+ breast cancer (1.36; 1.06–1.76), and none for ER−/PR- or ER−/PR+ breast cancers.