Using a dominant model stratification of the genotyping data according to tumour grade or histology revealed an interaction between rs3877899 (SEPP1) and rs1050450 (GPX1), with women who were heterozygous for both rs1050450 (CT) and rs3877899 (GA) being at increased risk of developing non-ductal breast cancer (OR = 2.94, 95%CI 1.35–6.37, p = 0.006, Table 4). The gene discussed is GPX1; the disease is breast cancer.