Reproductive factors and subtypes of breast cancer defined by estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2: a register-based study from Korea.

Abstract Background The relationship between reproductive breast risk factors and breast cancer survival in patients with different breast cancer subtypes is not well known. Methods We examined a large-sized, retrospective study of 23,882 subjects from the Korean Breast Cancer Registry. The breast cancer subtype was determined by immunohistochemical staining for estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 (HER2). Information regarding reproductive factors, including breastfeeding, age at first birth (AFB), and parity, was gathered. Multivariate Cox regression analysis was used to estimate the association among breast cancer subtypes, such as luminal A, luminal B, Her-2/neu overexpressing, and triple negative breast cancer (TNBC), and breast cancer survival as dependent variables and adjusting for age and stage. Results High parity (≥ 5) increased the recurrence risk of luminal A and B breast cancer (hazard ratio [HR], 1.95; 95% confidence interval [CI], 0.96-3.97; P  = .0055 and HR, 1.12; 95% CI, 0.42-3.02, respectively; P  = .0073) in breast cancer–specific survival (BCSS), but 1 to 3 child births decreased the recurrence risk of luminal A breast cancer (HR, 0.56; 95% CI, 0.34-0.91; P  = .0055) and luminal B breast cancer (HR, 0.32; 95% CI, 0.17-0.61; P  = .0073) in BCSS. Early AFB ( P  = .039) in BCSS and of TNBC (HR, 1.31; 95% CI, 0.78-2.21; P  = .0006) in overall survival. Her-2/neu overexpressing breast cancer had no correlation with parity and AFB in breast cancer survival. Conclusions High parity (≥ 5) and early AFB (