Risk factors for pregnancy-associated breast cancer: A report from the Nigerian Breast Cancer Study

Purpose: Little is known about risk factors for pregnancy-associated breast cancer (PABC), diagnosed during pregnancy or postpartum. Methods: We enrolled 1715 premenopausal women from the Nigerian Breast Cancer Study from 1998 to2011. Based on recency of last pregnancy from diagnosis, breast cancer cases were categorized as (1) PABC diagnosed 2 years or longer postpartum, (2) PABC diagnosed 3 to 5years postpartum, or (3) non-PABC diagnosed more than 5 years postpartum. Controls were matched to cases on recency of last pregnancy. Multiple logistic regressions were performed comparing cases and controls within eachgroup. Results: Of the 718 cases, 152 (21.2%) had PABC 2 or more years postpartum, and 145 (20.2%) 3 to 5years postpartum. Although not statistically significant, women with higher parity tend to have an elevated risk of PABC but reduced risk of non-PABC (p for heterogeneity=0.097). Family history of breast cancer might be a strong predictor particularly for PABC 2 or more years postpartum (odds ratio,3.28; 95% confidence interval, 1.05-10.3). Compared with non-PABC cases, PABC 2or more years postpartum cases were more likely to carry BRCA1/2 mutations (P= .03). Conclusions: Parity may have different roles in the development of PABC versus other premenopausal breast cancer in Nigerian women. Prospective mothers with multiple births and a family history of breast cancer may have an elevated risk of breast cancer during their immediate postpartum period. © 2013 Elsevier Inc.