Modify Breast Cancer Risk Research Articles

Retrospective analysis of estrogen receptor1 and N‑acetyltransferase gene expression in normal breast tissue, primary breast tumors, and established breast cancer cell lines.

The expression levels of estrogen receptor 1 (ESR1), arylamine N-acetyltransferase 1 (NAT1), and arylamine N-acetyltransferase 2 (NAT2) are implicated in breast cancer; however, their co-expression profiles in normal breast tissue, primary breast tumors and established breast cancer cell lines are undefined. NAT1 expression is widely reported to be associated with ESR1 expression and is frequently investigated in breast cancer etiology. Furthermore, the NAT2 phenotype has been reported to modify breast cancer risk in molecular epidemiological association studies. Understanding the relationships between the expression levels of these genes is essential to understand their role in breast cancer etiology and treatment. In the present study, NAT1, NAT2 and ESR1 expression data were accessed from repositories of RNA-Seq data covering 57 breast cancer cell lines, 1,043 primary breast tumors and 99 normal breast tissues. The relationships between gene expression, and between NAT1 activity and RNA expression in breast cancer cell lines were evaluated using non-parametric statistical analyses. Differences in gene expression in each dataset, as well as gene expression differences in normal breast tissue compared to primary breast tumors, and stratification by estrogen receptor status were determined. NAT1 and NAT2 mRNA expression were detected in normal and primary breast tumor tissues; NAT1 expression was much higher than NAT2. NAT1 and ESR1 expression were strongly associated, whereas NAT2 and ESR1 expression were not. Although NAT1 and NAT2 expression were associated, the magnitude was moderate. NAT1, NAT2, and ESR1 expression were increased in primary breast tumor tissue compared with normal breast tissue; however, the magnitude and significance of the differences were lower for NAT2. Analysis of NAT1, NAT2, and ESR1 expression in normal and primary breast tissues and breast cancer cell lines suggested that NAT1 and NAT2 expression are regulated by distinctive mechanisms, whereas NAT1 and ESR1 expression may have overlapping regulation. Defining these relationships is important for future investigations into breast cancer prevention.

Combining Variables for Cancer Risk Estimation: Is the Sum Better than the Parts?

Examining joint exposures of modifiable breast cancer risk factors may provide advantages over individual exposure-disease association analyses. Using the Healthy Lifestyle Index, Arthur and colleagues analyzed the joint impacts of diet, alcohol, smoking, physical activity, and obesity on breast cancer risk, and subtypes, in postmenopausal women enrolled in the Women's Health Initiative. The analysis provides data for population-attributable risk estimations and future prevention trials to target multiple risk factors. The public health messages for the individual risk factors remain unchanged, however, and it is still not clear whether improving one risk factor can counteract the adverse effects of another. Cancer Prev Res; 11(6); 313-6. ©2018 AACRSee related article by Arthur et al., p. 317.

Serum osteoprotegerin levels and mammographic density among high-risk women.

Mammographic density is a risk factor for breast cancer but the mechanism behind this association is unclear. The receptor activator of nuclear factor κB (RANK)/RANK ligand (RANKL) pathway has been implicated in the development of breast cancer. Given the role of RANK signaling in mammary epithelial cell proliferation, we hypothesized this pathway may also be associated with mammographic density. Osteoprotegerin (OPG), a decoy receptor for RANKL, is known to inhibit RANK signaling. Thus, it is of interest to evaluate whether OPG levels modify breast cancer risk through mammographic density. We quantified serum OPG levels in 57 premenopausal and 43 postmenopausal women using an enzyme-linked immunosorbent assay (ELISA). Cumulus was used to measure percent density, dense area, and non-dense area for each mammographic image. Subjects were classified into high versus low OPG levels based on the median serum OPG level in the entire cohort (115.1pg/mL). Multivariate models were used to assess the relationship between serum OPG levels and the measures of mammographic density. Serum OPG levels were not associated with mammographic density among premenopausal women (P ≥ 0.42). Among postmenopausal women, those with low serum OPG levels had higher mean percent mammographic density (20.9% vs. 13.7%; P = 0.04) and mean dense area (23.4 cm2 vs. 15.2 cm2; P = 0.02) compared to those with high serum OPG levels after covariate adjustment. These findings suggest that low OPG levels may be associated with high mammographic density, particularly in postmenopausal women. Targeting RANK signaling may represent a plausible, non-surgical prevention option for high-risk women with high mammographic density, especially those with low circulating OPG levels.

Mitochondrial DNA copy number variation, leukocyte telomere length, and breast cancer risk in the European Prospective Investigation into Cancer and Nutrition (EPIC) study

BackgroundLeukocyte telomere length (LTL) and mitochondrial genome (mtDNA) copy number and deletions have been proposed as risk markers for various cancer types, including breast cancer (BC).MethodsTo gain a more comprehensive picture on how these markers can modulate BC risk, alone or in conjunction, we performed simultaneous measurements of LTL and mtDNA copy number in up to 570 BC cases and 538 controls from the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. As a first step, we measured LTL and mtDNA copy number in 96 individuals for which a blood sample had been collected twice with an interval of 15 years.ResultsAccording to the intraclass correlation (ICC), we found very good stability over the time period for both measurements, with ICCs of 0.63 for LTL and 0.60 for mtDNA copy number. In the analysis of the entire study sample, we observed that longer LTL was strongly associated with increased risk of BC (OR 2.71, 95% CI 1.58–4.65, p = 3.07 × 10− 4 for highest vs. lowest quartile; OR 3.20, 95% CI 1.57–6.55, p = 1.41 × 10− 3 as a continuous variable). We did not find any association between mtDNA copy number and BC risk; however, when considering only the functional copies, we observed an increased risk of developing estrogen receptor-positive BC (OR 2.47, 95% CI 1.05–5.80, p = 0.04 for highest vs. lowest quartile).ConclusionsWe observed a very good correlation between the markers over a period of 15 years. We confirm a role of LTL in BC carcinogenesis and suggest an effect of mtDNA copy number on BC risk.

Are VNTRs co-localizing with breast cancer-associated SNPs?

Several common genetic variants (single-nucleotide polymorphisms, SNPs) have been shown to be associated with breast cancer (BC) risk in the general population, and to modify BC risk for BRCA1 and BRCA2 mutation carriers. Co-localization of variable number of tandem repeats (VNTRs) with these BC-associated SNPS has not been comprehensively studied. Cross referencing of genome-wide VNTRs with the known BC genome-wide association studies (GWAS) SNPs significantly associated with increased risk for developing breast cancer was carried out. Analysis was based on the overlap between the VNTRs and 10-kb windows around these BC-susceptibility SNPs. Cross referencing of the 1.2 million TR with the 161 known BC-associated SNPs in the general population led to 690 matches. Of those, in 17 VNTRs, the SNP was within the VNTR. Analysis restricted to loci known to modify BC penetrance in BRCA1 (n=31) and BRCA2 (n=33) mutation carriers led to 139 and 170 co-localization matches, respectively. For these, none of the SNPs were within the VNTR. The distances between the SNPs and the VNTRs were not significantly different from what was expected to occur by chance alone (p=0.61; p=0.44; p=0.25, respectively). There is no evidence that VNTRs co-localize with currently reported SNP tagged BC GWAS loci.

Pathway-based discovery of genetic interactions in breast cancer.

Breast cancer is the second largest cause of cancer death among U.S. women and the leading cause of cancer death among women worldwide. Genome-wide association studies (GWAS) have identified several genetic variants associated with susceptibility to breast cancer, but these still explain less than half of the estimated genetic contribution to the disease. Combinations of variants (i.e. genetic interactions) may play an important role in breast cancer susceptibility. However, due to a lack of statistical power, the current tests for genetic interactions from GWAS data mainly leverage prior knowledge to focus on small sets of genes or SNPs that are known to have an association with breast cancer. Thus, many genetic interactions, particularly among novel variants, remain understudied. Reverse-genetic interaction screens in model organisms have shown that genetic interactions frequently cluster into highly structured motifs, where members of the same pathway share similar patterns of genetic interactions. Based on this key observation, we recently developed a method called BridGE to search for such structured motifs in genetic networks derived from GWAS studies and identify pathway-level genetic interactions in human populations. We applied BridGE to six independent breast cancer cohorts and identified significant pathway-level interactions in five cohorts. Joint analysis across all five cohorts revealed a high confidence consensus set of genetic interactions with support in multiple cohorts. The discovered interactions implicated the glutathione conjugation, vitamin D receptor, purine metabolism, mitotic prometaphase, and steroid hormone biosynthesis pathways as major modifiers of breast cancer risk. Notably, while many of the pathways identified by BridGE show clear relevance to breast cancer, variants in these pathways had not been previously discovered by traditional single variant association tests, or single pathway enrichment analysis that does not consider SNP-SNP interactions.

Abstract 4240: Determination of normative patterns of gene expression levels and breast cancer risk biomarkers in human breast milk

Abstract Parity and breastfeeding influence a woman’s risk of developing breast cancer. Understanding the underlying molecular changes in the breast will facilitate identification of additional factors during pregnancy and postpartum that modify breast cancer risk. Most prior studies in humans on this topic, however, have been cross-sectional studies comparing breast tissue samples from nulliparous versus post-pregnant women, and are limited in their ability to characterize longitudinal changes and within-person variations. Breast milk contains cells of the mature gland, and may have a potential as a noninvasive source for studying molecular characteristics of the pregnancy-associated changes in the breast and their impact on breast cancer risk. The objectives of this study were to (1) determine normative patterns of gene expression levels in longitudinally collected breast milk samples and (2) correlate gene expression data in relation to self-reported measures of psychosocial stress during pregnancy and postpartum period. Our preliminary results showed that the post-pregnancy gene expression levels in breast milk samples can be measured reproducibly over a short period of time. Whole-genome transcriptome analysis revealed that expression levels of the post-pregnancy genes are different in early (less than 3 month postpartum) and late lactation period (more than 6 month postpartum). Moreover cytokine expression profiling correlated expression of inflammatory cytokines with early versus late postpartum period. The unique contribution of this study is to capture longitudinal gene expression data from breast milk samples collected over the course of lactation, hence providing a valuable basis for future studies to identify differential dynamics associated with breast cancer susceptibility. Note: This abstract was not presented at the meeting. Citation Format: Maria Ouzounova, Georgina Lewis, Raziye Piranlioglu, Tiana Curry-McCoy, Wonsuk Yoo, Nita Maihle, Sangmi Kim, Hasan Korkaya. Determination of normative patterns of gene expression levels and breast cancer risk biomarkers in human breast milk [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4240. doi:10.1158/1538-7445.AM2017-4240

Effects of lifestyle and diet as modifiers of risk of breast cancer (BC) in BRCA1 and BRCA2 carriers.

1505 Background: Mutations in the BRCA1/2 genes confer a high lifetime risk of BC. Penetrance varies among populations and individuals suggesting that non-genetic factors may modify the inherited risk. Knowledge of modifiable factors will help to develop preventive strategies. Methods: Information on physical activity (PA) (current PA and in the adolescence) and smoking was collected in 892 women (W) with a BRCA1/BRCA2 germ-line mutation (582 with BC, 45,62% BRCA2) from 279 families, followed at three Spanish Genetic Counseling Units, 481of these W also answered a food frequency questionnaire. Participants gave their consent and the study was approved by the ethics committee. The association between BC, lifestyle factors and dietary patterns (Mediterranean and Western) associated with BC were studied using logistic regression. Huber-White robust estimators of variance were employed to take into account correlations between family members. Age, menopausal status, specific mutated gene, BMI, parity and oral contraception were included as co-variables. BC was classified as HR+/+,- or HR-. Results: W who did PA daily had half the risk of BC than sedentary W (OR:0,53;p=0,043 for current PA;OR:0,40;p=0,007 for PA in the adolescent) and no differences were observed between BRCA1 and BRCA2 carriers. Also, W who daily exercised in both periods had a reduction of their BC risk (OR:0,22;p<0,001). The effect of PA was particularly important among premenopausal W (p-het<0,05). PA in the adolescent decreased the risk of all type of tumors. Nevertheless, alcohol intake, smoking habit and type of diet, did not significantly modify BC risk in this BRCA W. Conclusions: Our preliminary data suggest a clear reduction in BC risk among BRCA1/2 carriers who exercise regularly, mainly during the adolescence, and could be considered as potential modifiable factor for BC prevention in these group of W.

Study to determine whether SNPs in CYP17A1, ESR1, and TNRC9 loci correlate with increased breast cancer risk and serum 25-OH vitamin D levels.

e13086 Background: Low serum 25-OH vitamin D (25-OH Vit.D) level is associated with a higher risk of breast cancer. Many single nucleotide polymorphisms (SNP) are associated with breast cancer risk, although the mechanisms underlying this association in most cases remain unclear. We attempted to address this issue by determining whether specific SNPs were correlated with breast cancer-associated biomarkers (BM). Methods: We analyzed estrogen receptor (ER)-positive breast cancer patients treated between Jan 2011 and Dec 2014. We measured serum testosterone and 25-OH Vit.D in pre- and post-menopausal women, and also measured estradiol in the latter group. We genotyped 7 individual SNPs both in premenopausal and postmenopausal women. We then looked for correlations between BMs and SNPs in all three genotypes (homozygotes of major alleles, heterozygotes and homozygotes of minor alleles) using the Kruskal-Wallis test. For each SNP locus associated with a trend or significant effect with regard to BM levels, a t-test was then applied to determine which of the two genotypes was responsible for the effect. Results: Four hundred thirteen women were enrolled (163 premenopausal patients, and 250 postmenopausal patients). There was a trend difference between CYP17A1 rs743572 and 25-OH Vit.D (p = 0.0888), ESR1 rs204210 and 25-OH Vit.D (p = 0.0534) in premenopausal women, and a significant difference between TNRC9 rs3803662 and 25-OH Vit.D (p = 0.026) in postmenopausal women. Among premenopausal women, 25-OH Vit.D levels were significantly lower in those with the high-risk rs743572 genotype TC when compared with TT individuals (19.2 +/- 6.7 ng/ml vs 22.9 +/- 8.7 ng/ml; p = 0.0125). Similarly, 25-OH Vit.D was significantly lower in women with the high-risk rs204210 genotype AG when compared with GG individuals (19.1 +/- 6.9 ng/ml vs 21.7 +/- 6.4 ng/ml; p = 0.0219). In postmenopausal women, 25-OH Vit.D was significantly lower in women with the high-risk rs3803662 genotype GG than those with the AA genotype (20.5 +/- 9.2 ng/ml vs 24.4 +/- 8.0 ng/ml; p = 0.0104). Conclusions: Specific SNPs in CYP17A1, ESR1, and TNRC9 genes may modulate breast cancer risk due to their influence on serum 25-OH Vit.D levels.

Dietary Isoflavones and Breast Cancer Risk.

Breast cancer is the deadliest neoplasm in women globally, resulting in a significant health burden. In many cases, breast cancer becomes resistant to chemotherapy, radiation, and hormonal therapies. It is believed that genetics is not the major cause of breast cancer. Other contributing risk factors include age at first childbirth, age at menarche, age at menopause, use of oral contraceptives, race and ethnicity, and diet. Diet has been shown to influence breast cancer incidence, recurrence, and prognosis. Soy isoflavones have long been a staple in Asian diets, and there appears to be an increase, albeit modest, compared to Asian populations, in soy consumption among Americans. Isoflavones are phytoestrogens that have antiestrogenic as well as estrogenic effects on breast cancer cells in culture, in animal models, and in clinical trials. This study will investigate anticancer and tumor promoting properties of dietary isoflavones and evaluate their effects on breast cancer development. Furthermore, this work seeks to elucidate the putative molecular pathways by which these phytochemicals modulate breast cancer risk by synergizing or antagonizing the estrogen receptor (ER) and in ER-independent signaling mechanisms.

Highlights of This Issue

Highly active antiretroviral therapy (HAART) has extended the life expectancy of HIV/AIDS patients, but it remains unclear whether HIV infection affects the survival of lymphoma patients in the HAART era. Han and colleagues compared survival of lymphoma patients treated with HAART therapy. Among 179,520 lymphoma patients, HIV infection was significantly associated with inferior overall survival for patients with each lymphoma subtype, indicating that HIV/AIDS continues to be independently associated with increased risk of death among lymphoma patients in the HAART era in the United States.Adolescents and young adults (15 to 39 years old) with acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML) experience inferior survival when compared with children. Wolfson and colleagues examined the impact of care at NCI-designated Comprehensive Cancer Centers (CCC) or Children's Oncology Group sites (COG) on survival disparities. The authors report that adolescent and young adult ALL or AML patients at non-CCC/COG sites experienced inferior outcomes. Barriers to accessing specialized CCC/COG care include public insurance/uninsured, and African American and Hispanic race/ethnicity.Type II diabetes is associated with breast cancer risk in epidemiologic studies, and pregnancy also modifies breast cancer risk. Powe and colleagues hypothesized that women with a history of gestational diabetes mellitus (GDM) would have greater invasive breast cancer risk than parous women without a history of diabetes. The authors conducted a prospective analysis among parous women in the Nurses' Health Study II. Among 86,972 women studied, 5,188 women reported a history of GDM and 2,377 developed invasive breast cancer. Among this large cohort of U.S. women, a history of GDM was not associated with an elevated risk of subsequent invasive breast cancer.The neutrophil-to-lymphocyte ratio (NLR) is a cytological marker of both inflammation and poor outcomes in cancer patients. DNA methylation is a key element of the epigenetic program defining different leukocyte subtypes, and may provide an alternative to cytology in assessing leukocyte profiles. Koestler and colleagues created a bioinformatic tool to estimate NLR using DNA methylation and assessed its diagnostic and prognostic performance in human populations. The authors developed a DNA methylation-derived NLR (mdNLR) index based on normal isolated leukocyte methylation libraries and established cell-mixture deconvolution algorithms. Across cancer studies, mdNLR scores were either elevated in cases relative to controls, or associated with increased hazard of death, indicating our current understanding of mature leukocyte methylomes is sufficient to apply epigenetically based analyses of NLR in clinical and epidemiologic studies of cancer risk and survival.

History of Gestational Diabetes Mellitus and Risk of Incident Invasive Breast Cancer among Parous Women in the Nurses' Health Study II Prospective Cohort.

Background: Type II diabetes is associated with breast cancer in epidemiologic studies. Pregnancy also modifies breast cancer risk. We hypothesized that women with a history of gestational diabetes mellitus (GDM), which shares pathogenesis and risk factors with type II diabetes, would have greater invasive breast cancer risk than parous women without a history of GDM.Methods: We conducted a prospective analysis among parous women in the Nurses' Health Study II, with mean age 35 years in 1989. Multivariate Cox proportional hazards models were used to compare risks of incident invasive breast cancer in women with and without a history of GDM.Results: Among 86,972 women studied, 5,188 women reported a history of GDM and 2,377 developed invasive breast cancer (100 with history of GDM, 2,277 without GDM) over 22 years of prospective follow-up. History of GDM was inversely associated with incident invasive breast cancer [HR, 0.68; 95% confidence interval (CI), 0.55-0.84; P = 0.0004], compared with no history of GDM, after adjustment for body mass index, reproductive history, and other breast cancer risk factors. Findings were similar by menopausal status, although observed person-time was predominantly premenopausal (premenopausal: HR, 0.73; 95% CI, 0.56-0.96; P = 0.03; postmenopausal: HR, 0.63; 95% CI, 0.43-0.92; P = 0.02). Restricting to women undergoing mammography screening modestly attenuated the relationship (HR, 0.74; 95% CI, 0.57-0.96; P = 0.02).Conclusions: Among a large cohort of U.S. women, history of GDM was not associated with an elevated risk of subsequent invasive breast cancer.Impact: Our findings highlight the need to further investigate GDM's role in breast cancer development. Cancer Epidemiol Biomarkers Prev; 26(3); 321-7. ©2016 AACR.

Population Attributable Risk of Modifiable and Nonmodifiable Breast Cancer Risk Factors in Postmenopausal Breast Cancer.

We examined the proportions of multiple types of breast cancers in the population that were attributable to established risk factors, focusing on behaviors that are modifiable at menopause. We estimated the full and partial population attributable risk percentages (PAR%) by combining the relative risks and the observed prevalence rates of the risk factors of interest. A total of 8,421 cases of invasive breast cancer developed in postmenopausal women (n=121,700) in the Nurses' Health Study from 1980-2010. We included the following modifiable risk factors in our analyses: weight change since age 18 years, alcohol consumption, physical activity level, breastfeeding, and menopausal hormone therapy use. Additionally, the following nonmodifiable factors were included: age, age at menarche, height, a combination of parity and age at first birth, body mass index at age 18 years, family history of breast cancer, and prior benign breast disease. When we considered all risk factors (and controlled for age), the PAR% for invasive breast cancers was 70.0% (95% confidence interval: 55.0, 80.7). When considering only modifiable factors, we found that changing the risk factor profile to the lowest weight gain, no alcohol consumption, high physical activity level, breastfeeding, and no menopausal hormone therapy use was associated with a PAR% of 34.6% (95% confidence interval: 22.7, 45.4). The PAR% for modifiable factors was higher for estrogen receptor-positive breast cancers (PAR%=39.7%) than for estrogen receptor-negative breast cancers (PAR%=27.9%). Risk factors that are modifiable at menopause account for more than one-third of postmenopausal breast cancers; therefore, a substantial proportion of breast cancer in the United States is preventable.

An opportunity to address modifiable breast cancer risks: Mammography screening and physical activity readiness to change.

Breast cancer risk is significantly reduced by improvements in lifestyle factors such as physical activity. Previous work suggests personal experiences such as false positive mammography or family history of breast cancer may influence these health behaviors. Surveys were distributed to women aged 40–75 who had received a negative mammogram from an academic hospital in Virginia in 2015. Measures assessed breast cancer worry and perceived risk, awareness of cancer risk factors, family history of breast cancer, false positive mammography experience, and readiness to change physical activity. Surveys were collected from 106 women. The regression for readiness to change physical activity was significant, F(7, 91) = 3.7, p = 0.001, R2 = 0.22. Physical activity readiness to change was positively associated with income (p = 0.034) and receipt of a false positive mammogram (p = 0.045). African American women (p = 0.031) and women with family history of breast cancer (p = 0.027) reported lower readiness to change physical activity. Results support previous qualitative work suggesting the receipt of a false positive mammogram may stimulate motivation to increase physical activity. Mammography screening may serve as a strategic opportunity to target modifiable breast cancer risk factors at a time when women are highly receptive to a lifestyle change intervention.

Association of breast cancer risk in BRCA1 and BRCA2 mutation carriers with genetic variants showing differential allelic expression: identification of a modifier of breast cancer risk at locus 11q22.3

PurposeCis-acting regulatory SNPs resulting in differential allelic expression (DAE) may, in part, explain the underlying phenotypic variation associated with many complex diseases. To investigate whether common variants associated with DAE were involved in breast cancer susceptibility among BRCA1 and BRCA2 mutation carriers, a list of 175 genes was developed based of their involvement in cancer-related pathways.MethodsUsing data from a genome-wide map of SNPs associated with allelic expression, we assessed the association of ~320 SNPs located in the vicinity of these genes with breast and ovarian cancer risks in 15,252 BRCA1 and 8211 BRCA2 mutation carriers ascertained from 54 studies participating in the Consortium of Investigators of Modifiers of BRCA1/2.ResultsWe identified a region on 11q22.3 that is significantly associated with breast cancer risk in BRCA1 mutation carriers (most significant SNP rs228595 p = 7 × 10−6). This association was absent in BRCA2 carriers (p = 0.57). The 11q22.3 region notably encompasses genes such as ACAT1, NPAT, and ATM. Expression quantitative trait loci associations were observed in both normal breast and tumors across this region, namely for ACAT1, ATM, and other genes. In silico analysis revealed some overlap between top risk-associated SNPs and relevant biological features in mammary cell data, which suggests potential functional significance.ConclusionWe identified 11q22.3 as a new modifier locus in BRCA1 carriers. Replication in larger studies using estrogen receptor (ER)-negative or triple-negative (i.e., ER-, progesterone receptor-, and HER2-negative) cases could therefore be helpful to confirm the association of this locus with breast cancer risk.

The Non-coding Mammary Carcinoma Susceptibility Locus, Mcs5c, Regulates Pappa Expression via Age-Specific Chromatin Folding and Allele-Dependent DNA Methylation.

In understanding the etiology of breast cancer, the contributions of both genetic and environmental risk factors are further complicated by the impact of breast developmental stage. Specifically, the time period ranging from childhood to young adulthood represents a critical developmental window in a woman’s life when she is more susceptible to environmental hazards that may affect future breast cancer risk. Although the effects of environmental exposures during particular developmental Windows of Susceptibility (WOS) are well documented, the genetic mechanisms governing these interactions are largely unknown. Functional characterization of the Mammary Carcinoma Susceptibility 5c, Mcs5c, congenic rat model of breast cancer at various stages of mammary gland development was conducted to gain insight into the interplay between genetic risk factors and WOS. Using quantitative real-time PCR, chromosome conformation capture, and bisulfite pyrosequencing we have found that Mcs5c acts within the mammary gland to regulate expression of the neighboring gene Pappa during a critical mammary developmental time period in the rat, corresponding to the human young adult WOS. Pappa has been shown to positively regulate the IGF signaling pathway, which is required for proper mammary gland/breast development and is of increasing interest in breast cancer pathogenesis. Mcs5c-mediated regulation of Pappa appears to occur through age-dependent and mammary gland-specific chromatin looping, as well as genotype-dependent CpG island shore methylation. This represents, to our knowledge, the first insight into cellular mechanisms underlying the WOS phenomenon and demonstrates the influence developmental stage can have on risk locus functionality. Additionally, this work represents a novel model for further investigation into how environmental factors, together with genetic factors, modulate breast cancer risk in the context of breast developmental stage.

Dietary choline and betaine intake, choline-metabolising genetic polymorphisms and breast cancer risk: a case-control study in China.

Choline and betaine are essential nutrients involved in one-carbon metabolism and have been hypothesised to affect breast cancer risk. Functional polymorphisms in genes encoding choline-related one-carbon metabolism enzymes, including phosphatidylethanolamine N-methyltransferase (PEMT), choline dehydrogenase (CHDH) and betaine-homocysteine methyltransferase (BHMT), have important roles in choline metabolism and may thus interact with dietary choline and betaine intake to modify breast cancer risk. This study aimed to investigate the interactive effect of polymorphisms in PEMT, BHMT and CHDH genes with choline/betaine intake on breast cancer risk among Chinese women. This hospital-based case-control study consecutively recruited 570 cases with histologically confirmed breast cancer and 576 age-matched (5-year interval) controls. Choline and betaine intakes were assessed by a validated FFQ, and genotyping was conducted for PEMT rs7946, CHDH rs9001 and BHMT rs3733890. OR and 95 % CI were estimated using unconditional logistic regression. Compared with the highest quartile of choline intake, the lowest intake quartile showed a significant increased risk of breast cancer. The SNP PEMT rs7946, CHDH rs9001 and BHMT rs3733890 had no overall association with breast cancer, but a significant risk reduction was observed among postmenopausal women with AA genotype of BHMT rs3733890 (OR 0·49; 95 % CI 0·25, 0·98). Significant interactions were observed between choline intake and SNP PEMT rs7946 (P interaction=0·029) and BHMT rs3733890 (P interaction=0·006) in relation to breast cancer risk. Our results suggest that SNP PEMT rs7946 and BHMT rs3733890 may interact with choline intake on breast cancer risk.

Abstract 2691: Genome-wide association study identifies two susceptibility loci that modify radiation-related risk for breast cancer after childhood cancer: A report from the Childhood Cancer Survivor Study and St. Jude Lifetime Cohort

Abstract Background: Childhood cancer survivors treated with chest radiotherapy have substantially elevated risk for developing breast cancer. Although numerous breast cancer susceptibility variants have been established, genetic predisposition for breast cancer after childhood cancer remains poorly understood. Methods: We conducted the first genome-wide association study of subsequent breast cancer in female childhood cancer survivors within two large-scale cohorts with detailed treatment data and systematic, long-term follow-up: the Childhood Cancer Survivor Study [CCSS; 178 breast cancer cases, 2200 controls (survivors without subsequent neoplasm) of European descent] and the St. Jude Lifetime Cohort (SJLIFE; 29 cases, 574 controls). Genotyping on the Illumina HumanOmni5MExome (CCSS) or Affymetrix 6.0 (SJLIFE) array and imputation based on the 1000 Genomes Project yielded >16 million high quality genotyped or imputed variants available in both studies. Assuming an additive genetic model, we used multivariate Cox regression to quantify the effect of each variant in the overall population and stratified by receipt of ≥10 Gray (Gy) or <10 Gy radiation exposure to the chest. Results: We identified two loci associated with breast cancer risk among children who received ≥10 Gy radiation to the chest (131 cases, 493 controls): one at 1q41 [rs4342822, risk allele frequency (RAF) = 0.46 in controls, pooled per allele hazard ratio (HR) = 1.94, 95% confidence interval (CI) = 1.50-2.51, Pexact = 1.20×10−8] and another at 11q23 (rs74949440, RAF = 0.02 in controls, HR = 3.71, 95%CI = 2.18-6.32, Pexact = 2.00×10−9). Neither locus was associated with breast cancer risk among children who received <10 Gy radiation to the chest (69 cases, 2144 controls; rs4342822: HR = 1.03, 95%CI = 0.75-1.44; rs74949440: HR = 1.21, 0.41-3.54). Results were consistent in the two studies, and the associations did not appear to be related to type of first primary childhood cancer. Both loci fall in or near biologically plausible candidate genes: the variant rs4342822 lies near PROX1, which is amplified in >10% of breast cancers in The Cancer Genome Atlas data. The variant rs74949440 is intronic to TAGLN, whose expression levels have been associated with breast cancer prognosis and altered cell death resistance following irradiation in human carcinoma cell lines. Conclusion: These findings represent the first evidence outside of identified high-risk cancer susceptibility genes that certain individuals are genetically predisposed to developing breast cancer after radiotherapy and suggest that radiation exposure may interact with germline genetics to modify breast cancer risk. Citation Format: Lindsay M. Morton, Joshua N. Sampson, Gregory T. Armstrong, Ting-Huei Chen, Melissa Hudson, Eric Karlins, Casey L. Dagnall, Shenchao Li, Carmen L. Wilson, Kumar Srivastava, Wei Liu, Guolian Kang, Kevin Oeffinger, Tara O. Henderson, Chaya S. Moskowitz, Todd M. Gibson, Diana M. Merino, Jeannette R. Wong, Sue Hammond, Joseph P. Neglia, Lucie M. Turcotte, Jeremy Miller, Laura Bowen, William A. Wheeler, Wendy M. Leisenring, John A. Whitton, Laurie Burdette, Belynda D. Hicks, Mitchell J. Machiela, Aurelie Vogt, Zhaoming Wang, Meredith Yeager, Geoffrey Neale, Matthew Lear, Louise C. Strong, Yutaka Yasui, Marilyn Stovall, Rita E. Weathers, Susan A. Smith, Rebecca Howell, Stella M. Davies, Gretchen A. Radloff, Amy Berrington de González, Peter D. Inskip, Preetha Rajaraman, Joseph F. Fraumeni, Smita Bhatia, Stephen J. Chanock, Margaret A. Tucker, Leslie L. Robison. Genome-wide association study identifies two susceptibility loci that modify radiation-related risk for breast cancer after childhood cancer: A report from the Childhood Cancer Survivor Study and St. Jude Lifetime Cohort. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2691.

XRCC1 Gene Polymorphisms and Breast Cancer Risk: A Systematic Review and Meta- Analysis Study.

Breast cancer risk assessment has developed during years and evaluation of genetic factor affecting risk of breast cancer is an important component of this risk assessment. The aim of this meta-analysis was to investigate the role of XRCC1 polymorphisms (Arg194Trp, Arg280His and Arg399Gln) for risk of breast cancer among different population and categories of menopausal status. PubMed, Medline, Web of Science, and PubMed Central were systematically searched to identify studies evaluating association between breast cancer and XRCC1 gene polymorphisms (Arg194Trp, Arg280His and Arg399Gln). Two authors independently extracted required information. Odds Ratios were pooled for four genetic inheritance models using both fixed and the DerSimonian and Laird random-effect models. Egger's test and contour-enhanced funnel plot were used to evaluate publication bias and small study effect. Additional subgroup analysis was performed for menopausal status, ethnicity, and source of controls. After evaluation and applying inclusion criteria on extracted studies, fifty three studies were included in this meta-analysis. For polymorphisms of Arg194Trp and Arg280His, no significant association was observed in all genetic models. Arg194Trp had a protective effect in post-menopausal status only in homozygote model (OR=0.57 [0.37-0.88]). Arg399Gln showed significant association with breast cancer in homozygote (OR=1.21 [1.10-1.34]), dominant (OR=1.09 [1.03-1.15]) and recessive (OR=1.21 [1.09-1.35]) models. Arg399Gln was associated with higher risk in post-menopausal status for homozygote and heterozygote models. Our findings suggest that XRCC1 gene polymorphisms modify breast cancer risk in different populations and different categories of menopausal status.

Interaction between APC and Fen1 during breast carcinogenesis.

Aberrant DNA base excision repair (BER) contributes to malignant transformation. However, inter-individual variations in DNA repair capacity plays a key role in modifying breast cancer risk. We review here emerging evidence that two proteins involved in BER - adenomatous polyposis coli (APC) and flap endonuclease 1 (Fen1) - promote the development of breast cancer through novel mechanisms. APC and Fen1 expression and interaction is increased in breast tumors versus normal cells, APC interacts with and blocks Fen1 activity in Pol-β-directed LP-BER, and abrogation of LP-BER is linked with cigarette smoke condensate-induced transformation of normal breast epithelial cells. Carcinogens increase expression of APC and Fen1 in spontaneously immortalized human breast epithelial cells, human colon cancer cells, and mouse embryonic fibroblasts. Since APC and Fen1 are tumor suppressors, an increase in their levels could protect against carcinogenesis; however, this does not seem to be the case. Elevated Fen1 levels in breast and lung cancer cells may reflect the enhanced proliferation of cancer cells or increased DNA damage in cancer cells compared to normal cells. Inactivation of the tumor suppressor functions of APC and Fen1 is due to their interaction, which may act as a susceptibility factor for breast cancer. The increased interaction of APC and Fen1 may occur due to polypmorphic and/or mutational variation in these genes. Screening of APC and Fen1 polymorphic and/or mutational variations and APC/Fen1 interaction may permit assessment of individual DNA repair capability and the risk for breast cancer development. Such individuals might lower their breast cancer risk by reducing exposure to carcinogens. Stratifying individuals according to susceptibility would greatly assist epidemiologic studies of the impact of suspected environmental carcinogens. Additionally, a mechanistic understanding of the interaction of APC and Fen1 may provide the basis for developing new and effective targeted chemopreventive and chemotherapeutic agents.