Int J Cancer

Few risk factors have been identified for triple negative breast cancer (TNBC) which lacks expression of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2). This more aggressive subtype disproportionately affects some racial/ethnic minorities and is associated with lower survival. We pooled data from three population-based studies (558 TNBC and 5,111 controls) and examined associations of TNBC risk with reproductive history and breast-feeding. We estimated odds ratios (ORs) and 95% confidence intervals (CIs) using multivariable logistic regression. For younger women, aged <50 years, TNBC risk was increased two-fold for parous women who never breast-fed compared to nulliparous women (OR\u2009=\u20092.02, 95% CI\u2009=\u20091.12-3.63). For younger parous women, longer duration of lifetime breast-feeding was associated with a borderline reduced risk ( 6524 vs. 0 months: OR\u2009=\u20090.52, 95% CI\u2009=\u20090.26-1.04, P| \u2009=\u20090.06). Considering the joint effect of parity and breast-feeding, risk was increased two-fold for women with 653 full-term pregnancies (FTPs) and no or short-term (<12 months) breast-feeding compared to women with 1-2 FTPs and breast-feeding 6512 months (OR\u2009=\u20092.56, 95% CI\u2009=\u20091.22-5.35). None of these associations were observed among older women ( 6550 years). Differences in reproductive patterns possibly contribute to the ethnic differences in TNBC incidence. Among controls aged