PGR and breast cancer: Relative to controls, women with PSE< 5 cigarettes per day, and those with PSE ≥ 5 cigarettes per day, had increased breast cancer risk with ORs of 1.42 (95% CI: 0.91–2.22) and 2.20 (95% CI: 1.32–3.65), respectively, in the ER+/PR+ group (P = 0.009).