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 ERPR+, 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 z30 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 ERPR tumors (OR, 1.1; 95 % CI, 0.8-1.6). Women who gained z30 kg in weight during adulthood had an f3-fold increased relative risk of ER+PR+ tumors (OR, 2.7; 95 % CI, 1.9-3.8), but no risk increase of ERPR tumors (OR, 1.0; 95 % CI, 0.5-2.1), compared with women who gained <10 kg. Compared with never users, women who used menopausal estrogen-progestin therapy for at least 5 years were at increased risk of ER+PR+ tumors (OR, 3.0; 95 % CI, 2.1-4.1) but not ERPR tumors (OR, 1.3; 95 % CI, 0.7-2.5). In conclusion, other risk factors were similarly related to breast cancer regardless of receptor status, but high age at first birth, substantial weight gain in adult age, and use of menopausal estrogen-progestin therapy were more strongly related to receptor-positive breast cancer than receptor-negative breast cancer. (Cancer Epidemiol Biomarkers Prev 2006;15(12):2482–8