ERBB2 and neoplasm: For the subgroup analyses, among non-breastfeeding cases, parity of at least three children was associated with a statistically significant increased likelihood of having a triple-negative tumor (OR = 1.68; 95% CI = 1.00 to 2.81) and a Her2-overexpressing tumor (OR = 3.03; 95% CI = 1.27 to 7.23) compared with luminal A. In contrast, no differential associations of breastfeeding and parity were observed among luminal B cases.