Significant differences between case and control groups are evident for the following variables, smoking habit (P = .000388), family history of breast cancer (P = .00001), use of OCs (P = .0291) and use of hormone replacement therapy (HRT) (P = .00001), parity (P = .0128), and breastfeeding (P = .0265); BRCA1 or BRCA2 mutations also show differences between case and control groups (P < .0001). This evidence concerns the gene BRCA1 and breast cancer.