Risk Factors for Hormone Receptor-Defined Breast Cancer in Postmenopausal Women

The effect of classic breast cancer risk factors on hormone receptor-defined breast cancer is not fully clarified. We explored these associations in a Swedish population-based study. Postmenopausal women ages 50 to 74 years, diagnosed with invasive breast cancer during 1993 to 1995, were compared with 3,065 age frequency-matched controls. We identified 332 estrogen receptor (ER − ) and progesterone receptor (PR − ) negative, 286 ER + PR − , 71 ER − PR + , 1,165 ER + PR + , and 789 tumors with unknown receptor status. Unconditional logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals (95% CI). Women ages ≥30 years, compared with those ages 20 to 24 years at first birth, were at an increased risk of ER + PR + tumors (OR, 1.5; 95% CI, 1.2-1.8) but not ER − PR − tumors (OR, 1.1; 95% CI, 0.8-1.6). Women who gained ≥30 kg in weight during adulthood had an ∼3-fold increased relative risk of ER + PR + tumors (OR, 2.7; 95% CI, 1.9-3.8), but no risk increase of ER − PR − tumors (OR, 1.0; 95% CI, 0.5-2.1), compared with women who gained