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Cancer Sci. 2012 Oct;103(10):1861-70. doi: 10.1111/j.1349-7006.2012.02379.x. Epub 2012 Aug 8.

Reproductive factors and breast cancer risk in relation to hormone receptor and menopausal status in Japanese women.

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1
Division of Community Health, Tohoku University Graduate School of Medicine, Sendai, Japan.

Abstract

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 (P(trend) = 0.0016 for ER+/PgR+; P(trend) = 0.015 for ER-/PgR-) and among postmenopausal women (P(trend) = 0.012 for ER+/PgR+; P(trend) = 0.0056 for ER-/PgR-). Nulliparity was associated with an increased risk of ER+/PgR+, but not ER-/PgR- cancer among women overall (P(heterogeneity) = 0.019) and among postmenopausal women (odds ratio for ER+/PgR+ = 2.56, 95% confidence interval = 1.61-4.07; P(heterogeneity) = 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.

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