SEARCH

SEARCH BY CITATION

The associations between menstrual and reproductive factors and breast cancer risk in relation to estrogen/progesterone receptor (ER/PgR) status have been unclear in Japanese women. This case-control study evaluated these associations, overall and separately, by menopausal status. A total of 1092 breast cancer cases and 3160 controls were selected from among female patients aged 30 years and over admitted to a single hospital in Miyagi Prefecture between 1997 and 2009. The receptor status distribution among the cases (missing: 8.4%) was 571 ER+/PgR+, 133 ER+/PgR−, 24 ER−/PgR+ and 271 ER−/PgR−. Menstrual and reproductive factors were assessed using a self-administered questionnaire. Polytomous logistic regression and tests for heterogeneity across ER+/PgR+ and ER−/PgR− were conducted. Later age at menarche was significantly associated with a decreased risk of both ER+/PgR+ and ER−/PgR− cancer among women overall (Ptrend = 0.0016 for ER+/PgR+; Ptrend = 0.015 for ER−/PgR−) and among postmenopausal women (Ptrend = 0.012 for ER+/PgR+; Ptrend = 0.0056 for ER−/PgR−). Nulliparity was associated with an increased risk of ER+/PgR+, but not ER−/PgR− cancer among women overall (Pheterogeneity = 0.019) and among postmenopausal women (odds ratio for ER+/PgR+ = 2.56, 95% confidence interval = 1.61–4.07; Pheterogeneity = 0.0095). A longer duration of breastfeeding tended to be associated with a decreased risk in all subtypes among women overall. Later age at menarche has a protective effect against both ER+/PgR+ and ER−/PgR− cancer. However, parity might impact differently on various subtypes of breast cancer. Further studies are needed to clarify the etiology of the rare ER+/PgR− and ER−/PgR+ cancer subtypes.