CYP17, catechol-o-methyltransferase, and glutathione transferase M1 genetic polymorphisms, lifestyle factors, and breast cancer risk in women on Prince Edward Island.

Genetic polymorphisms in enzymes controlling the formation and disposition of estrogens and their metabolites have been shown to influence breast cancer risk. Environmental and lifestyle factors may interact with estrogen metabolism polymorphisms to influence breast cancer risk. We studied the role of lifestyle factors and genetic polymorphisms in estrogen metabolism in women from Prince Edward Island (PEI), a small province of 135,000 people on the east coast of Canada. Women (207 cases; 621 controls) were matched on age, menopausal status, and family history of breast cancer. The predominant lifestyle risk factors previously reported to influence breast cancer risk such as body mass index (BMI), parity, and smoking had similar influences in the PEI population. Genetic polymorphisms in CYP17, GSTM1, and catechol-O-methyltransferase (COMT) were not associated with a general increase in breast cancer risk. However, the CYP17 A2/A2 genotype was only observed in women with estrogen receptor (ER) positive breast cancer and not in ER negative breast cancer. The increased risk associated with elevated BMI was only observed in women homozygous for the CYP17 and COMT reference alleles. Similarly, the increased risk associated with extended use of oral contraceptives (≥ 15years), was only observed in women homozygous for the reference alleles of CYP17 and COMT. The GSTM1 homozygous gene deletion was associated with a significantly increased risk of breast cancer in postmenopausal women with a family history of breast cancer risk. These results suggest the polymorphic genes that control estrogen formation and disposition interact significantly with other risk factors to influence breast cancer risk.