A case-only study on 282 women with breast cancer found that smokers carrying the SULT1A1 638 A allele had a two-fold increase in risk compared to non-smokers carrying the SULT1A1 638GG genotype (OR = 2.55, 95%CI: 1.21–5.36), and smokers carrying the CYP1B1 1294G allele also had a higher risk of breast cancer than non-smokers carrying the 1294CC genotype (OR = 2.32, 95%CI: 1.00–5.38) [34]. Here, SULT1A1 is linked to breast cancer.