Breastfeeding and Risk of Breast Cancer: Case-Control Study.

The aim of this study was to investigate a possible association of breast cancer occurrence in women with their breastfeeding experience. A matched case-control study was conducted in Kragujevac, Serbia. A total of 382 women (191 cases with breast cancer and 191 controls) were interviewed, but the data were explored on breastfeeding and breast cancer only among parous women (339 women). Logistic regression was used to calculate odds ratios (ORs) as estimates of the relative risk of breast cancer. Compared with controls, significantly more cases ever breastfed [adjusted OR (ORadj) = 2.90, 95 percent confidence interval (95 percent CI) 1.02-8.22], breastfed all their children (ORadj = 2.93; 95 percent CI 1.03-8.29), and had longer lifetime duration of breastfeeding (ORadj = 3.44, 95 percent CI 1.15-10.24 for 13 or more months). In comparison with controls, significantly more cases breastfed at first birth (ORadj = 3.17, 95 percent CI 1.36-7.37). Breast cancer risk increased if first breastfeeding occurred at an older age (p for trend = .042) and with longer duration of breastfeeding (p for trend = .037). Our study is one of the few in which breastfeeding was found to be a risk factor for breast cancer.