Polymorphisms in circadian genes, night work and breast cancer: results from the GENICA study.

OBJECTIVES: The role of genetic variants and environmental factors in breast cancer etiology has been intensively studied in the last decades. Gene-environment interactions are now increasingly being investigated to gain more insights into the development of breast cancer, specific subtypes, and therapeutics. Recently, night shift work that involves circadian disruption has gained rising interest as a potential non-genetic breast cancer risk factor. Here, we analyzed genetic polymorphisms in genes of cellular clocks, melatonin biosynthesis and signaling and their association with breast cancer as well as gene-gene and gene-night work interactions in a German case-control study on breast cancer. METHODS: GENICA is a population-based case-control study on breast cancer conducted in the Greater Region of Bonn. Associations between seven polymorphisms in circadian genes (CLOCK, NPAS2, ARTNL, PER2 and CRY2), genes of melatonin biosynthesis and signaling (AANAT and MTNR1B) and breast cancer were analyzed with conditional logistic regression models, adjusted for potential confounders for 1022 cases and 1014 controls. Detailed shift-work information was documented for 857 breast cancer cases and 892 controls. Gene-gene and gene-shiftwork interactions were analyzed using model-based multifactor dimensionality reduction (mbMDR). RESULTS: For combined heterozygotes and rare homozygotes a slightly elevated breast cancer risk was found for rs8150 in gene AANAT (OR 1.17; 95% CI 1.01-1.36), and a reduced risk for rs3816358 in gene ARNTL (OR 0.82; 95% CI 0.69-0.97) in the complete study population. In the subgroup of shift workers, rare homozygotes for rs10462028 in the CLOCK gene had an elevated risk of breast cancer (OR for AA vs. GG: 3.53; 95% CI 1.09-11.42). Shift work and CLOCK gene interactions were observed in the two-way interaction analysis. In addition, gene-shiftwork interactions were detected for MTNR1B with NPAS2 and ARNTL. CONCLUSIONS: In conclusion, the results of our population-based case-control study support a putative role of the CLOCK gene in the development of breast cancer in shift workers. In addition, higher order interaction analyses suggest a potential relevance of MTNR1B with the key transcriptional factor NPAS2 with ARNTL. Hence, in the context of circadian disruption, multivariable models should be preferred that consider a wide range of polymorphisms, e.g. that may influence chronotype or light sensitivity. The investigation of these interactions in larger studies is needed.

CYP2B6*6 is associated with increased breast cancer risk.

The cytochrome P450 2B6 (CYP2B6) is involved in the metabolism of testosterone. Functional changes in this enzyme may influence endogenous hormone exposure, which has been associated with risk of breast cancer. To assess potential associations between two functional polymorphisms CYP2B6_516_G>T (rs3745274) and CYP2B6_785_A>G (rs2279343) and breast cancer risk, we established a specific matrix-assisted laser desorption/ionization time-of-flight mass spectrometry assay. The GENICA breast cancer case-control study showed associations between the variant genotypes CYP2B6_516_TT and CYP2B6_785_GG and breast cancer risk with odds ratios (ORs) of 1.34 (p = 0.001) and 1.31 (p = 0.002), respectively. A similar effect was observed for carriers of the CYP2B6_516_T allele in a validation study including four independent studies from Germany, Sweden and USA. In a pooled analysis of all five studies involving 4,638 breast cancer cases and 3,594 controls of European ancestry, carriers of the CYP2B6_516_G and the CYP2B6_785_G variant had an increased breast cancer risk with ORs of 1.10 (p = 0.027) and 1.10 (p = 0.031), respectively. We conclude that the genetic variants CYP2B6_516_G and CYP2B6_785_G (designated CYP2B6*6), which are known to decrease activity of the CYP2B6 enzyme, contribute to an increased breast cancer risk.

The UGT1A6_19_GG genotype is a breast cancer risk factor.

Validation of an association between the UGT1A6_19_T>G (rs6759892) polymorphism and overall breast cancer risk. A pilot study included two population-based case-control studies from Germany (MARIE-GENICA). An independent validation study comprised four independent breast cancer case-control studies from Finland (KBCP, OBCS), Germany (BBCC), and Sweden (SASBAC). The pooled analysis included 7418 cases and 8720 controls from all six studies. Participants were of European descent. Genotyping was done by MALDI-TOF MS and statistical analysis was performed by logistic regression adjusted for age and study. The increased overall breast cancer risk for women with the UGT1A6_19_GG genotype which was observed in the pilot study was confirmed in the set of four independent study collections (OR 1.13, 95% CI 1.05-1.22; p = 0.001). The pooled study showed a similar effect (OR 1.09, 95% CI 1.04-1.14; p = 0.001). The risk effect on the basis of allele frequencies was highly significant, the pooled analysis showed an OR of 1.11 (95% CI 1.06-1.16; p = 5.8 × 10(-6)). We confirmed the association of UGT1A6_19_GG with increased overall breast cancer risk and conclude that our result from a well powered multi-stage study adds a novel candidate to the panel of validated breast cancer susceptibility loci.

Night work and breast cancer estrogen receptor status--results from the German GENICA study.

OBJECTIVES: The potential mechanisms that link night-shift work with breast cancer have been extensively discussed. Exposure to light at night (LAN) depletes melatonin that has oncostatic and anti-estrogenic properties and may lead to a modified expression of estrogen receptor (ER) α. Here, we explored the association between shift work and breast cancer in subgroups of patients with ER-positive and -negative tumors. METHODS: GENICA (Gene-ENvironment Interaction and breast CAncer) is a population-based case-control study on breast cancer with detailed information on shift work from 857 breast cancer cases and 892 controls. ER status was assessed by immunohistochemical staining. Associations between night-shift work and ER-positive and -negative breast cancer were analyzed with conditional logistic regression models, adjusted for potential confounders. RESULTS: ER status was assessed for 827 cases and was positive in 653 and negative in 174 breast tumors. Overall, 49 cases and 54 controls were "ever employed" in shift work including night shifts for ≥ 1 year. In total, "ever shift work" and "ever night work" were not associated with an elevated risk of ER-positive or -negative breast tumors. Night work for ≥ 20 years was associated with a significantly elevated risk of ER-negative breast cancer [odds ratio (OR) 4.73, 95% confidence interval (95% CI) 1.22-18.36]. CONCLUSIONS: Our case-control study suggests that long-term night-shift work is associated with an increased risk of ER-negative breast cancers. Further studies on histological subtypes and the analysis of other potentially relevant factors are crucial for discovering putative mechanisms.

Confirmation of the reduction of hormone replacement therapy-related breast cancer risk for carriers of the HSD17B1_937_G variant.

17ß-hydroxysteroid dehydrogenase type 1 (HSD17B1) plays an important role in the biosynthesis of 17ß-estradiol. The current study aimed at confirming the reduced risk of breast cancer in carriers of the non-synonymous HSD17B1_937_A>G (rs605059) polymorphism who used any hormone replacement therapy (HRT) for 10 years or longer. We performed an independent association study using four breast cancer case-control studies from Australia, Germany, and Sweden. In all, 5,777 cases and 8,189 age-matched controls of European descent were genotyped by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and TaqMan. Risk estimates were calculated by interaction analysis and main effect analysis adjusted for age and study. Main effect analyses for women using any HRT for 10 years or longer (1,428 cases versus 1,724 controls) revealed a protective effect of the HSD17B1_937_G allele on breast cancer risk (OR 0.86, 95 % CI: 0.73-0.99; p = 0.048). Thus, our previous finding of a protective effect of the HSD17B1_937_G allele on HRT-associated breast cancer risk has now been confirmed both in independent large patient cohorts and a comprehensive pooled analysis supporting the hypothesis that a HSD17B1-mediated decreased conversion of estrone to the more potent 17ß-estradiol may reduce the estrogenic effects, thereby reducing the risk of developing breast cancer during long-term HRT use.

Exploring the association between genetic variation in the SUMO isopeptidase gene USPL1 and breast cancer through integration of data from the population-based GENICA study and external genetic databases.

Small ubiquitin-like modifier (SUMO) proteins are covalently attached to target proteins to modify their function. SUMO conjugation participates in processes tightly linked to tumorigenesis. Recently USPL1 (ubiquitin-specific peptidase-like (1) was identified as a SUMO isopeptidase. We report here on the first exploratory study investigating the relationship between genetic variability in USPL1 and breast cancer. Three potentially functional nonsynonymous coding SNPs (rs3742303, rs17609459, rs7984952) were genotyped in 1,021 breast cancer cases and 1,015 controls from the population-based GENICA study. We took advantage of multiple genotype imputation based on HapMap and the 1000 Genomes Project data to refine the association screening in the investigated region. Public genetic databases were also used to investigate the relationship with USPL1 expression in lymphoblastoid cell lines and breast tissue. Women homozygous for the minor C allele of rs7984952 showed a lower risk of Grade 3 breast tumors compared to TT homozygotes (OR 0.50, 95% CI 0.30-0.81). Case-only analyses confirmed the association between rs7984952 and tumor grade (OR 0.60, 95% CI 0.39-0.93). Imputation results in a 238 kb region around rs7984952 based on HapMap and the 1000 Genomes Project data were similar. No imputed variant showed an association signal stronger than rs7984952. USPL1 expression in tumor breast tissue increased with the number of C alleles. The present study illustrates the contribution of multiple imputation of genotypes using public data repositories to standard genotyping laboratory. The provided information may facilitate the design of independent studies to validate the association between USPL1 rs7984952 and risk of Grade 3 breast tumors.

The earwax-associated SNP c.538G>A (G180R) in ABCC11 is not associated with breast cancer risk in Europeans.

Genetic polymorphisms of human ABC-transporter genes have been suggested to modulate breast cancer risk in the general population. In particular ABCC11 (MRP8), which is highly expressed in breast cancer tissue and involved in the efflux of conjugated estrogen metabolites such as estrone-3-sulfate and estradiol-17beta-glucuronide, has recently been proposed as a potential risk factor for female breast cancer. The wet earwax-associated G-allele of the c.538G>A polymorphism was associated with an increased risk for breast cancer in Japanese women. In contrast, no evidence for such an association could be observed in Caucasian women. We aimed to confirm/refute the association of the c.538G>A variant in ABCC11 with breast cancer risk and/or histo-pathological tumor characteristics in an independent population-based breast cancer case-control study from Germany comprising 1021 cases and 1015 age-matched controls. No association for allele and genotype frequencies of the 538G>A variant in ABCB11 with breast cancer risk was found. Our data suggest that the c.538G>A variation in ABCC11 does not contribute to breast carcinogenesis in women of European descent.

No association of polymorphisms in the cell polarity gene SCRIB with breast cancer risk.

The human homolog of the Drosophila Scribble (SCRIB) tumor suppressor gene encodes a protein that regulates apical-basolateral polarity in mammalian epithelia and controls cell proliferation. Due to the role of cell polarity proteins in human cancers, we investigated whether genetic variability in SCRIB impacts breast carcinogenesis and tumor pathology. Five genetic variants were analyzed for an association with breast cancer risk and histopathological tumor parameters using a single nucleotide polymorphism (SNP) tagging approach. Genotyping of five tag SNPs was performed by TaqMan allelic discrimination and RFLP-based PCR using the GENICA population-based breast cancer case-control collection including 1,021 cases and 1,015 age-matched controls. Odds ratios (OR) and 95% confidence intervals (CI) were calculated by ordinal logistic regression. None of the tag SNPs was associated with breast cancer risk or tumor characteristics. Our findings suggest that genetic variability in the SCRIB polarity gene does not contribute to breast cancer development.

Polymorphisms of the nuclear receptor pregnane X receptor and organic anion transporter polypeptides 1A2, 1B1, 1B3, and 2B1 are not associated with breast cancer risk.

Organic anion transporter polypeptides (OATPs, SLCOs) are involved in the uptake of conjugates steroid hormones such as estrone-3-sulfate. It has been suggested that the expression of OATPs in breast tissues could impact breast carcinogenesis and tumor pathology. The nuclear receptor pregnane X receptor (PXR) is involved in the regulation of SLCO1A2 expression. We investigated 31 variants located in PXR, SLCO1A2, SLCO1B1, SLCO1B3, and SLCO2B1 for an association with breast cancer risk and/or histo-pathological tumor characteristics. Polymorphisms were selected on the basis of a known or potential functional consequence and an allele frequency >2%. Genotyping was performed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry using the GENICA population-based breast cancer case-control collection comprising 1,021 cases and 1,015 age-matched controls. Statistical analysis was performed by SAS, and all tests were two-sided. None of the 31 analyzed transporter and PXR polymorphisms showed an association with breast cancer risk or tumor characteristics. Our data suggest that among the many known transporters common variations of PXR, SLCO1A2, SLCO1B1, SLCO1B3, and SLCO2B1 do not contribute to breast carcinogenesis.

Polymorphisms in the UBC9 and PIAS3 genes of the SUMO-conjugating system and breast cancer risk.

SUMOylation consists in the covalent conjugation of small ubiquitin-related modifiers to target proteins. SUMOylation participates in processes that are tightly linked to tumorigenesis, and genetic variability in the SUMO-conjugating system may influence the development of breast cancer. We recently reported that variation in the UBC9 gene encoding the SUMO-conjugating enzyme may affect the grade of breast tumors. Following comprehensive in silico analyses for detection of putative functional polymorphisms in 14 genes of the SUMO system, we selected one coding SNP in PIAS3 and seven tag SNPs in UBC9 for association analyses. Results were based on 1,021 cases, and 1,015 matched controls from the population-based GENICA study. Odds ratios (OR) and 95% confidence intervals (CI) were estimated by conditional logistic regression. To explore the association with polymorphisms closely linked to the genotyped variants, multiple imputation based on HapMap data was applied. The study revealed associations of four UBC9 polymorphisms with risk of grade 1 tumors. Comparison of genotype and haplotype models indicated that the best representation of risk solely relied on rs7187167 under dominant penetrance. Women carrying the rare allele showed an increased risk of grade 1 tumors compared with common homozygotes (OR 1.87, 95% CI 1.18-2.95). This effect appeared to be stronger in women with a family history of breast or ovarian cancer. Imputation of polymorphisms in a 300-kb region around the genotyped polymorphisms identified no variants with stronger associations. Our findings suggest that genetic variation in UBC9 may affect the risk of grade 1 breast tumors.

No evidence for glutathione S-transferases GSTA2, GSTM2, GSTO1, GSTO2, and GSTZ1 in breast cancer risk.

Breast cancer is a complex disease and in recent years a number of breast cancer susceptibility genes have been identified, but the role of low penetrance susceptibility genes has not been completely resolved. Glutathione S-transferases (GSTs) are phase II xenobiotic metabolizing enzymes involved in the detoxification of chemical carcinogens and environmental pollutants and play an important role in cell defense mechanisms against oxidative stress. They have been in the spot light for the investigation of a potential association with breast cancer risk but so far, sparse or even no data for a potential contribution of GSTA2, GSTM2, GSTO, and GSTZ to breast cancer risk are available. We genotyped GSTA2_448_C > G (rs2180314), GSTA2_742_A > C (rs6577), GSTM2_-832_T > C (rs638820), GSTO1_-1242_G > A (rs2164624), GSTO1_419_A > C (rs4925), GSTO2_-183_A > G (rs2297235), GSTO2_342_A > G (rs156697), GSTZ1_-4378_A > G (rs1046428), and GSTZ1_94_G > A (rs3177427) by MALDI-TOF MS in the German GENICA breast cancer case-control collection of 1021 cases and 1015 controls and performed breast cancer risk association in general and with respect to the stratifications: menopausal status, family history of breast or ovarian cancer, use of oral contraceptives, use of hormone therapy, body mass index, and smoking as well as histopathological tumor characteristics including hormone receptor status, grade, histology, and node status. We did not observe any breast cancer risk associations and conclude that it is unlikely that glutathione S-transferases GSTA2, GSTM2, GSTO1, GSTO2, and GSTZ1 participate in breast cancer susceptibility.

Night work and breast cancer - results from the German GENICA study.

OBJECTIVES: Some epidemiological and animal data indicate that night work might increase the risk for breast cancer. We have investigated the risk in a German population-based case-control study known as GENICA (gene environment interaction and breast cancer). METHODS: The GENICA study involved interviews to assess shift work information in 857 breast cancer cases and 892 controls. We estimated risks of employment status and night shift characteristics using conditional logistic regression models, adjusting for potential confounders. Resampling and bootstrapping were applied to adjust the risk estimates for a potential selection bias. RESULTS: Among 1749 women, 56 cases and 57 controls worked in night shifts for > or =1 year, usually in the healthcare sector (63.0% of controls). Female night workers were more frequently nulliparous and low-educated than day workers (28.6% versus 17.8% and 12.3% versus 9.2%, respectively). Fewer women in night work had ever used post-menopausal hormone therapy (35.7% versus 51.9%). An elevated breast cancer risk was not associated with having ever done shift or night work when compared to women employed in day work only [odds ratio (OR) 0.96, 95% confidence interval (95% CI) 0.67-1.38 and OR 0.91, 95% CI 0.55-1.49, respectively). Women who reported >807 night shifts, the third quartile of the distribution among controls, experienced a breast cancer risk of 1.73 (95% CI 0.71-4.22). Night work for > or =20 years was associated with an OR of 2.48 (95% CI 0.62-9.99) based on 12 cases and 5 controls. CONCLUSIONS: Long-term night work was associated with a modestly, but not significantly, increased breast cancer risk, while having ever done night work was not. The precision of the results was limited by a low prevalence of night work in this study population.

N-acetyltransferase 2, exposure to aromatic and heterocyclic amines, and receptor-defined breast cancer.

The role of N-acetyltransferase 2 (NAT2) polymorphism in breast cancer is still unclear. We explored the associations between potential sources of exposure to aromatic and heterocyclic amines (AHA), acetylation status and receptor-defined breast cancer in 1020 incident cases and 1047 population controls of the German GENICA study. Acetylation status was assessed as slow or fast. Therefore, NAT2 haplotypes were estimated using genotype information from six NAT2 polymorphisms. Most probable haplotypes served as alleles for the deduction of NAT2 acetylation status. The risks of developing estrogen receptor alpha (ER) and progesterone receptor (PR)-positive or negative tumors were estimated for tobacco smoking, consumption of red meat, grilled food, coffee, and tea, as well as expert-rated occupational exposure to AHA with logistic regression conditional on age and adjusted for potential confounders. Joint effects of these factors and NAT2 acetylation status were investigated. Frequent consumption of grilled food and coffee showed higher risks in slow acetylators for receptor-negative tumors [grilled food: ER-: odds ratio (OR) 2.57, 95% confidence interval (CI) 1.07-6.14 for regular vs. rare; coffee: ER-: OR 2.55, 95% CI 1.22-5.33 for >or=4 vs. 0 cups/day]. We observed slightly higher risks for never smokers that are fast acetylators for receptor-positive tumors compared with slow acetylators (ER-: OR 1.32, 95% CI 1.00-1.73). Our results support differing risk patterns for receptor-defined breast cancer. However, the modifying role of NAT2 for receptor-defined breast cancer is difficult to interpret in the light of complex mixtures of exposure to AHA.

Common variants in the UBC9 gene encoding the SUMO-conjugating enzyme are associated with breast tumor grade.

UBC9 encodes a protein that conjugates small ubiquitin-related modifier (SUMO) to target proteins resulting in a change of their localization, activity or stability. Genetic variability may affect expression and activity of UBC9 and may have an impact on breast tumor progression. We investigated associations between UBC9 genotypes and histopathological parameters in 1,021 breast cancer cases of the GENICA collection using a single nucleotide polymorphism (SNP) tagging approach. Genotyping analyses were performed by TaqMan(R) allelic discrimination. Odds ratios (OR) and 95% confidence intervals (CI) were calculated by ordinal logistic regression. Multiple imputation based on HapMap data was applied to boost the power of the study. The study revealed significant associations of three UBC9 SNPs with histological grade (rs7187167, p(trend) = 0.001; rs11248866, p(trend) = 0.009; rs8052688, p(trend) = 0.008). Model selection identified a recessive penetrance model for rs7187167 as the best representation of tumor grade (global p = 0.001). This model did not improve by inclusion of additional SNPs in linkage disequilibrium. Imputation of SNPs in a 300 kb region around the genotyped SNPs supported rs7187167 as a major contributor to tumor grade. Compared with common allele carriers, rare homozygotes presented less frequently with high grade tumors (G3 vs. G1: OR 0.26, 95% CI 0.11-0.62; G3 vs. G2: OR 0.45, 95% CI 0.23-0.86). In addition to tumor size, nodal status and estrogen receptor status, multivariate analyses confirmed an independent role of rs7187167 as predictor of tumor grade (p = 0.0003). The present results underline the value of genetic variation in UBC9 for breast cancer prognosis.

Polymorphic loci of E2F2, CCND1 and CCND3 are associated with HER2 status of breast tumors.

Overexpression of the human epidermal growth factor receptor 2 (HER2) in breast tumors is associated with bad prognosis. Therefore, it is highly relevant to further improve understanding of the regulatory mechanisms of HER2 expression. In addition to gene amplification, transcriptional regulation plays a crucial role in HER2 overexpression. In this study, we analyzed 3 polymorphisms E2F2_-5368_A>G, CCND1_870_A>G and CCND3_-677_C>T located in genes involved in cell cycle regulation in the GENICA population-based and age-matched breast cancer case-control study from Germany. We genotyped 1,021 cases and 1,015 controls by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Statistical analyses were performed by conditional logistic regression. We observed no differences in genotype frequencies between breast cancer cases and controls. Subgroup analysis showed associations between carriers of the E2F2_-5368_G allele (OR: 0.60, 95% CI: 0.42-0.85), carriers of the CCND1_870_G allele (OR: 0.66, 95% CI: 0.45-0.96) and carriers of the CCND3_-677_T allele (OR: 1.72, 95% CI: 1.20-2.49) and HER2 expression in breast tumors. This finding points to an association of an increased expression of these cell cycle regulators with lower expression of HER2. An explanation for this observation might be that low expression of E2F2, CCND1 and CCND3 decrease levels of factors down-regulating HER2. We conclude that the analyzed polymorphisms located in E2F2, CCND1 and CCND3 are potential markers for HER2 status of breast tumors.

Expression of heregulin, phosphorylated HER-2, HER-3 and HER-4 in HER-2 negative breast cancers.

A significant number of HER-2 amplified breast cancers is effectively treated by trastuzumab and further shows receptor-enhanced chemosensitivity. Recent studies have postulated transactivation of HER-2 also in tumors expressing phosphorylated/activated HER-2 (pHER-2) and of the HER-3/HER-4 ligand heregulin (HRG), independent of HER-2 amplification. As a consequence, a subset of tumors without HER-2 overexpression would be sensitive to trastuzumab chemotherapy. To investigate the potential transactivation of HER-2, in 171 breast cancers from the GENICA study with negative/low expression of HER-2 we analyzed the expression of pHER-2, HRG, HER-3 and HER-4 by immunohistochemistry. None of the tumors examined displayed expression of pHER-2. Moderate or strong cytoplasmic staining of HRG, HER-3 and HER-4 was observed in 44 (26%), 67 (39%) and 33 (19%) cases, respectively. No association of HRG, HER-3 and HER-4 with the survival of patients or with known prognostic clinical factors was seen. In conclusion, our data obtained on a well-characterized cohort of breast cancers provide no evidence of HER-2-activation in the absence of HER-2 overexpression. The biological function and clinical implications of HRG, HER-3 and HER-4 in this group of tumors remain unclear. Our results cannot support the hypothesis of a transactivation of HER-2 and thus a possible therapeutic benefit of trastuzumab in HER-2 negative breast cancers.

CYP2C19*17 is associated with decreased breast cancer risk.

Cytochrome P450 2C19 (CYP2C19) plays an important role in the metabolism of xenobiotics and drugs and contributes to the catabolism of endogenous substrates like estradiol. Genetic variability impacts expression and activity of CYP2C19 and therefore can influence catabolism of estrogens. In the present study we analyzed the association of three polymorphisms of CYP2C19 namely CYP2C19*2 (CYP2C19_681_G>A, rs4244285), CYP2C19*3 (CYP2C19_636_G>A, rs57081121) and CYP2C19*17 (CYP2C19_-806_C>T, rs12248560), with breast cancer susceptibility. We genotyped 1,015 breast cancer cases and 1,021 age-matched, population-based controls of the German GENICA study by matrix assisted laser desorption/ionization time-of-flight mass spectrometry. Risk estimates were calculated by logistic regression. All tests were two-sided. We observed a decreased breast cancer risk for carriers of the CYP2C19*17 allele (OR 0.77, 95% CI: 0.65-0.93; P = 0.005). In subgroup analysis we observed a significant decreased breast cancer risk for women using hormone therapy for ten years or longer who were carriers of the CYP2C19*17 allele (OR 0.57, 95% CI: 0.39-0.83; P = 0.003). Since CYP2C19*17 defines an ultra rapid metabolizer phenotype we suggest that an increased catabolism of estrogens by CYP2C19 may lead to decreased estrogen levels and therefore reduces breast cancer risk. This protective effect seems to be stronger in combination with long-term intake of supplemental estrogens during hormone therapy.

The CYP1B1_1358_GG genotype is associated with estrogen receptor-negative breast cancer.

Cytochrome P450 1B1 (CYP1B1) is a major enzyme in the initial catabolic step of estradiol (E2) metabolism and belongs to the multitude of genes regulated by the estrogen receptor alpha (ERalpha). The common non-synonymous polymorphisms CYP1B1_1358_A>G and CYP1B1_1294_C>G increase CYP1B1 enzymatic activity. Given a relationship between CYP1B1 and breast tumor E2 level as well as E2 level and breast tumor ERalpha expression it is of interest to know whether CYP1B1 polymorphisms have an impact on the ERalpha status of breast cancer. We genotyped the GENICA population-based breast cancer case-control collection (1,021 cases, 1,015 controls) by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and investigated in cases the association between genotypes and tumor ERalpha status (739 ERalpha positive cases; 212 ERalpha negative cases) by logistic regression. We observed a significant association between the homozygous variant CYP1B1_1358_GG genotype and negative ERalpha status (P = 0.005; OR 2.82, 95% CI: 1.37-5.82) with a highly significant Ptrend for CYP1B1_1358_A>G and negative ERalpha status (P = 0.003). We also observed an association of CYP1B1_1358_GG and negative PR status (P = 0.015; OR 2.36, 95% CI: 1.18-4.70) and a Ptrend of 0.111 for CYP1B1_1358_A>G and negative progesterone receptor (PR) status. We conclude that the CYP1B1_1358_A>G polymorphism has an impact on ERalpha status in breast cancer in that the CYP1B1_1358_GG genotype known to encode higher CYP1B1 activity is associated with ERalpha negativity.