A case-control study of reproductive factors associated with subtypes of breast cancer in Northeast China.

Based on the expression of estrogen receptor (ER), progesterone receptor (PR) and HER2/neu (HER2), breast cancer is classified into several subtypes: luminal A (ER+ and/or PR+, HER2-), luminal B (ER+ and/or PR+, HER2+), HER2-overexpressing (ER-, PR-, and HER2+) and triple-negative (ER-, PR-, and HER2-). The aim of this case-control study is to determine reproductive factors associated with breast cancer subtypes in Chinese women. A total of 1,417 patients diagnosed with breast cancer in the First Affiliated Hospital, China Medical University, Shenyang, China between 2001 and 2009 and 1,587 matched controls without a prior breast cancer were enrolled. Personal interviews were conducted to obtain information on reproductive characteristics and clinical history. Relationships between the factors and the subtypes of breast cancer were examined using logistic regression to compute odds ratios (OR) and 95% confidence intervals (CI). Notably, luminal A (50.0%) was the most prevalent subtype relative to luminal B (15.10%), HER2-overexpressing (10.87%) and triple-negative (23.08%). Menarche at an early age was associated with a reduced risk of luminal A (OR, 2.35; 95% CI, 1.45-3.81). Breastfeeding protected parous women from any subtype of breast cancer. Postmenopause and spontaneous abortion were inversely associated with the risk of luminal tumors. By contrast, multiparity, family history of breast cancer and induced abortion increased the risk of breast cancer. Collectively, our findings suggest that reproductive factors such as age at menarche, parity, breastfeeding, menopausal status and abortion history have different effects on the subtypes of breast cancer in Chinese women.