CYP3A Variation, Premenopausal Estrone Levels, and Breast Cancer Risk

Nichola Johnson, Kate Walker, Lorna J. Gibson, Nick Orr, Elizabeth Folkerd, Ben Haynes, Claire Palles, Ben Coupland, Minouk Schoemaker, Michael Jones, Peter Broderick, Elinor Sawyer (+16 others)
2012 Journal of the National Cancer Institute  
and Introduction Abstract Background Epidemiological studies have provided strong evidence for a role of endogenous sex steroids in the etiology of breast cancer. Our aim was to identify common variants in genes involved in sex steroid synthesis or metabolism that are associated with hormone levels and the risk of breast cancer in premenopausal women. Methods We measured urinary levels of estrone glucuronide (E1G) using a protocol specifically developed to account for cyclic variation in
more » ... levels during the menstrual cycle in 729 healthy premenopausal women. We genotyped 642 single-nucleotide polymorphisms (SNPs) in these women; a single SNP, rs10273424, was further tested for association with the risk of breast cancer using data from 10 551 breast cancer case patients and 17 535 control subjects. All statistical tests were two-sided. Results rs10273424, which maps approximately 50 kb centromeric to the cytochrome P450 3A (CYP3A) gene cluster at chromosome 7q22.1, was associated with a 21.8% reduction in E1G levels (95% confidence interval [CI] = 27.8% to 15.3% reduction; P = 2.7 × 10 −9 ) and a modest reduction in the risk of breast cancer in case patients who were diagnosed at or before age 50 years (odds ratio [OR] = 0.91, 95% CI = 0.83 to 0.99; P = .03) but not in those diagnosed after age 50 years (OR = 1.01, 95% CI = 0.93 to 1.10; P = .82). Conclusions Genetic variation in noncoding sequences flanking the CYP3A locus contributes to variance in premenopausal E1G levels and is associated with the risk of breast cancer in younger patients. This association may have wider implications given that the most predominantly expressed CYP3A gene, CYP3A4, is responsible for metabolism of endogenous and exogenous hormones and hormonal agents used in the treatment of breast cancer. Subjects and Methods Study Subjects Mammography, Oestrogens, and Growth Factors (MOG) Study. Full details of the MOG study have been published previously. [20] Briefly, this is an observational study nested within a trial of annual mammography screening in young women that was conducted in Britain. [21] Approximately 54 000 women aged 39-41 years were randomly assigned to the intervention arm from 1991 to 1997 and offered annual mammograms until age 48 years. From 2000 to 2003, women in the intervention arm who were still participating in this trial were invited to participate in the MOG study: They were asked to provide a blood sample and complete a questionnaire detailing demographic, lifestyle, and reproductive factors. More than 8000 women were enrolled in the study. A total of 520 women from the MOG study provided urine samples for the cross-sectional analysis of hormones ( Figure 1 ). All of the women included in this analysis reported being of Northern European ancestry, and none had been diagnosed with breast cancer at the time of study recruitment. Figure 1. Sample and single-nucleotide polymorphism (SNP) exclusion schema. Numbers of samples (n) and numbers of SNPs (N) analyzed for the cross-sectional analysis of hormone levels and the case-control analysis are shown. Of 691 SNPs that were genotyped, 642 (92.9%) were tested for association with hormone levels in up to 763 samples. A single SNP, rs10235235, that tags rs10273424 (r 2 = 1.0) was taken forward to a case-control analysis in combined data from five case-control series totaling 10 551 breast cancer case patients and 17 535 control subjects. BBCS = British Breast Cancer study; BGS = Breakthrough Generations Study; BIGGS = Breast Cancer in Galway Genetic Study; CGEMS = Cancer Genetic Markers of Susceptibility Study; DHEA = dehydroepiandrosterone; DHEAS = dehydroepiandrosterone sulfate; E1G = creatinine-adjusted urinary estrone glucuronide; HWE = Hardy-Weinberg Equilibrium; MOG = Mammography Oestrogens and Growth Factors study; PG = creatinine-adjusted pregnanediol glucuronide; SHBG = sex hormone-binding globulin; SNPs = single-nucleotide polymorphisms; WTCCC = Wellcome Trust Case-Control Consortium. British Breast Cancer Study (BBCS). Full details of the BBCS have been published previously. [22] Briefly, the BBCS is a national case-control study of breast cancer in which cases of breast cancer were ascertained through the cancer registries of England and Scotland and through the National Cancer Research Network. Breast cancer patients younger than age 71 years at diagnosis (mean age at diagnosis = 52.4 years, SD = 9.2 years) were recruited between 2001 and 2010. Case patients were asked to invite a healthy female first-degree relative with no history of cancer and a female friend or non-blood relative to participate in the study. A total of 567 healthy women who were first-degree relatives, friends, or non-blood relatives of the case patients provided urine samples for the cross-sectional analysis of hormones; a total of 4911 case patients and 2045 friends and non-blood relatives of the case patients participated in the case-control analysis. All breast cancer case patients and control subjects reported being of Northern European ancestry, and all control subjects were free from breast cancer by self-report at the time of study recruitment. Breast Cancer In Galway Genetic Study (BIGGS). BIGGS is a case-control study of breast cancer that is based in Western Ireland. [23] Recruitment was between 1998 and 2008. Case patients were ascertained through the University College Hospital Galway, and control subjects were drawn from the same Western Irish population. The mean age at diagnosis of case patients was 52.3 years (SD = 11.3 years). All control subjects were aged 60 years or older and had no personal history of cancer and no family history of breast or ovarian cancer in a first-or second-degree relative. A total of 950 case patients and 875 control subjects from BIGGS were included in the case-control analysis (Figure 1 ). All breast cancer case patients and control subjects reported being of Northern European ancestry. Breakthrough Generations Study (BGS) . BGS is a cohort study of more than 110 000 women from the UK general population, who were recruited beginning in 2003 and from whom detailed questionnaires and blood samples have been collected to investigate risk factors for breast cancer. [24] The study participants included prevalent breast cancer case patients who were diagnosed before entry into the study. Breast cancer diagnosis was self-reported. The mean age at breast cancer diagnosis was 50.8 years (SD = 9.4 years). A total of 3782 case patients and 4541 control subjects were included in the case-control analysis ( Figure 1 ). All breast cancer case patients and control subjects reported being of Northern European ancestry and all control subjects were free from breast cancer by self-report at the time of recruitment. Collection of blood samples and questionnaire information from all case patients and control subjects was undertaken with written informed consent and relevant ethical review board approval (MOG, BBCS, and BGS: ) in accordance with the tenets of the Declaration of Helsinki. Cross-sectional Analysis of Hormone Levels Eligible premenopausal women ascertained through the MOG study and relatives of case patients (one relative per case patient) and control subjects participating in the BBCS were invited to participate in this crosssectional analysis by providing serial urine samples at prespecified days during their menstrual cycle. To be eligible, women had to be having regular menstrual cycles (ie, their usual cycle length had to be between 21 and 35 days), not using hormone replacement therapy or oral contraceptives, and not have been diagnosed with breast cancer at recruitment to the study. The protocol for measuring follicular and luteal phase urinary E1G and PG has been published previously. [20] Briefly, E1G is a principal metabolite of the serum estrogens and, when measured in early morning urine samples, is highly correlated with the serum E2 curve, with a delay of 1-2 days (25, 26) . A woman's predicted date of ovulation was estimated from the date of the first day of her last menstrual period and her usual cycle length; ovulation was predicted to occur 14 days before the date of her next cycle. On the basis of this estimate, women were asked to provide an early morning urine sample on
doi:10.1093/jnci/djs156 pmid:22472546 fatcat:j4bd4ezszzhchfldmyuwpu5rnm