Background: Cytochrome P450 1A1 (CYP1A1) is involved in the 2-hydroxylation of estrogen, the hormone that plays a critical role in the etiology of breast carcinoma.
Methods: The authors evaluated common polymorphisms in the CYP1A1 gene in relation to breast carcinoma risk in a large population-based case-control study among Chinese women, the Shanghai Breast Cancer Study. Because the CYP1A1*3 and CYP1A1*4 alleles were not detected in the study population, analyses were performed for CYP1A1*2A (T-->C transition in the 3' noncoding region) and CYP1A1*2C (A-->G transition in exon 7, resulting in a substitution of Val for Ile) in 1134 patients with breast carcinoma and 1227 controls.
Results: The frequencies of the variant allele were 38.3% and 38.8% among cases and controls (P = 0.91), respectively, for the CYP1A1*2A polymorphism, and 23.1% and 24.8% (P = 0.26) for the CYP1A1*2C polymorphism. Homozygosity for both variant alleles in these 2 polymorphic sites (CYP1A1*2B) was associated with a borderline significant odds ratio (OR) of 0.71 (95% confidence interval [CI], 0.47-1.06). The reduced risk was more pronounced among postmenopausal women with long duration (> 30 yrs) of menstruation (OR = 0.43; 95% CI, 0.19-0.99) or among women with a low waist-to-hip ratio (OR = 0.52; 95% CI, 0.28-0.94).
Conclusions: Results from the current study suggest that homozygosity for the CYP1A1*2A and CYP1A1*2C alleles in the CYP1A1 gene may be associated with a reduced risk for breast carcinoma, particularly among lean women with long-term endogenous estrogen exposure.