Association of CYP 1 B 1 Polymorphisms and Breast Cancer Risk 1

Cytochrome P450 1B1 catalyzes the conversion of 17estradiol (E2) to the catechol estrogen metabolites 2-OHE2 and 4-OH-E2 that have been postulated to be involved in mammary carcinogenesis. We sought to determine whether two common functional polymorphisms in Cytochrome P450 1B1, V432L (m1), and A453S (m2) are related to breast cancer risk. Using a nested case control design within the Nurses’ Health Study cohort, we genotyped 453 cases and 456 controls and found no significant association between m1[val/leu and leu/leu versus val/val, OR 1 (CI, 0.72–1.45)] or m2 [asn/ser and ser/ser versus asn/asn, OR 0.8 (CI, 0.62–1.15)] and breast cancer risk. However, we did observe women with the Val/Val (m1) genotype to have a higher percentage of estrogen receptor-positive tumors (P 0.03). We did not observe any correlation with the m2 genotypes and estrogen receptor status. The association of the m1 and m2 genotypes on plasma hormone levels in postmenopausal control women not using hormone replacement therapy was also evaluated. Carriers of the m1 leu and m2 ser alleles had modestly higher estradiol levels but similar estrone and estrone sulfate levels. The results presented do not support a strong association between m1 and m2 and the risk of breast cancer. Introduction E2 is thought to have a role in mammary carcinogenesis. E2 is metabolized by either formation of the catechol estrogen derivatives 2-OH-E2 and 4-OH-E2 or by C-16hydroxylation. The CYP1B1 enzyme predominately catalyzes the formation of 4-OH-E2 (1–3), the most carcinogenic estrogen in animal models (4). Unlike the 2-OH-E2 derivative, 4-OH-E2 induces uterine adenocarcinoma (5) and can induce DNA single-strand breaks (6). In one study, human breast cancer tissue had a significantly higher ratio of 4-OH-E2/2-OH-E2 compared with adjacent normal tissue (7). In human breast cancer cell lines, the formation of 4-OH-E2 is inducible by dioxin, a common environmental contaminant (8). Although CYP1B1 is expressed in a wide variety of tissues, expression is particularly high in the breast, prostate, and uterus (9, 10), supporting a role for CYP1B1 in hormone-mediated cancer. These findings underscore the importance of the CYP1B1 with regard to metabolism of environmental carcinogens and estrogens and its potential role in the initiation of tumors in estrogen-responsive organs, like the breast. Two polymorphisms have been examined in relation to breast cancer risk, the m1 allele (Val to Leu at codon 432) and the m2 allele (Asn to Ser at codon 453). Recently, biochemical studies determined that the Val allele and the Asn allele had higher catalytic efficiency for the 4-hydroxylation of estradiol compared with their wild-type counterparts (11, 12). Changes in 4-hydroxylation of 17 -estradiol are of particular interest because of the potential carcinogenicity and estrogenic activity of the 4-OH-E2. In a case control study, Bailey et al. (13), found no association with the m1 and m2 alleles and breast cancer risk. They did, however, find an association between the m1 Val/Val genotype and Caucasian breast cancer patients who had ERpositive breast cancer (P 0.02); no correlation with the m2 allele was noted (13). In a second case control study of 186 Asian breast cancer cases and 200 Asian controls, the authors found that women with the m1 Leu/Leu genotype had a 2-fold elevated risk of breast cancer compared with women with the Val/Val genotype (14). This lack of consistency may be attributable to ethnic differences among studies. These authors were unable to evaluate receptor status. In this study, we evaluated, among primarily Caucasian women, the relationship between the CYP1B1 alleles and breast cancer risk in a nested case control study within the NHS cohort. Given the role of CYP1B1 in estradiol metabolism, we also evaluated the relationship between the m1 and m2 alleles and circulating estrogen levels. Materials and Methods Study Population. The NHS was initiated in 1976, when 121,700 United States registered nurses between the ages of 30 and 55 returned an initial questionnaire reporting medical histories and baseline health-related exposures. Between 1989 and 1990, blood samples were collected from 32,826 women. Incident breast cancers are identified by self-report and confirmed by medical record review. Eligible cases in this study consisted of women diagnosed with pathologically confirmed incident breast cancer after giving a blood specimen up to June 1, 1994. Controls were matched to cases on year of birth, menopausal status, and postmenopausal hormone use, as well as time of day, month, and fasting status at blood draw; menopause was defined as described previously (15). The nested case control study consists of 453 incident breast cancer cases and 456 matched controls. The study sample for the plasma hormone Received 10/12/01; revised 2/15/02; accepted 2/24/02. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 Supported by NIH Grants CA65725, CA87969, and CA49449 I.D. is partially supported by a grant from the American Cancer Society (RPG-00-061-01-CCE). 2 To whom requests for reprints should be addressed, at Channing Laboratory, 181 Longwood Avenue, Boston, MA 02115. E-mail: Devivo@channing.harvard.edu. 3 The abbreviations used are: E2, 17-estradiol; ER, estrogen receptor; CYP1B1, cytochrome P450 1B1; NHS, Nurses’ Health Study; OR, odds ratio; CI, confidence interval; BMI, body mass index. 489 Vol. 11, 489–492, May 2002 Cancer Epidemiology, Biomarkers & Prevention