Objective: It has been suggested that functional polymorphisms in genes encoding tobacco carcinogen-metabolizing enzymes may modify the relationship between tobacco smoking and breast cancer risk. We sought to determine if there is a gene-environment interaction between GSTM I (GSTM1A and GSTM1B), and GSTT1 genotypes and cigarette smoking in the risk of breast cancer.
Methods: Cases and controls were recruited in a case-control study conducted in Connecticut from 1994 to 1998. Cases were histologically confirmed, incident breast cancer patients, and controls were randomly selected from women histologically confirmed to be without breast cancer. A total of 338 cases and 345 controls were genotyped for GSTM1 and GSTT1 .
Results: None of the GSTM 1 genotypes, either alone or in combination with cigarette smoking, was associated with breast cancer risk. There was, however, a significantly increased risk of breast cancer among postmenopausal women with a GSTTI null genotype (OR= 1.9, 95% CI 1.2-2.9). There were also indications of increased risk of breast cancer associated with cigarette smoking for postmenopausal women with GSTT1-null genotype, especially for those who commenced smoking before age 18 (OR = 2.9, 95% CI 1.0-8.8).
Conclusion: Women with a GSTT1-null genotype may have an increased breast cancer risk, especially postmenopausal women who started smoking at younger ages.