Identification of a breast cancer susceptibility locus at 4q31.22 using a genome-wide association study paradigm

Fine-mapping of a novel premenopausal breast cancer susceptibility locus at Chr4q31.22 in Caucasian women and validation in African and Chinese women

We previously identified a novel breast cancer susceptibility variant on chromosome 4q31.22 locus (rs1429142) conferring risk among women of European ancestry. Here, we report replication of findings, validation of the variant in diverse populations and fine-mapping of the associated locus in Caucasian population. The SNP rs1429142 (C/T, minor allele frequency 18%) showed association for the overall breast cancer risk in Stages 1-4 (n = 4,331 cases/4271 controls; p = 4.35 × 10^-8 ; odds ratio, OR_C-allele ,1.25), and an elevated risk among premenopausal women (n = 1,503 cases/4271 controls; p = 5.81 × 10^-10 ; OR_C-allele 1.40) in European populations. SNP rs1429142 was associated with premenopausal breast cancer risk in women of African (T/C; p-value 1.45 × 10^-02 ; OR_C-allele 1.2) but not from Chinese ancestry. Fine-mapping of the locus revealed several potential causal variants which are present within a single association signal, revealed from the conditional regression analysis. Functional annotation of the potential causal variants revealed three putative SNPs rs1366691, rs1429139 and rs7667633 with active enhancer functions inferred based on histone marks, DNase hypersensitive sites in breast cell line data. These putative variants were bound by transcription factors (C-FOS, STAT1/3 and POL2/3) with known roles in inflammatory pathways. Furthermore, Hi-C data revealed several short-range interactions in the fine-mapped locus harboring the putative variants. The fine mapped locus was predicted to be within a single topologically associated domain, potentially facilitating enhancer-promoter interactions possibly leading to the regulation of nearby genes.

Breast cancer associated germline structural variants harboring small noncoding RNAs impact post-transcriptional gene regulation

Copy Number Variants (CNVs) are a class of structural variations of DNA. Germline CNVs are known to confer disease susceptibility, but their role in breast cancer warrants further investigations. We hypothesized that breast cancer associated germline CNVs contribute to disease risk through gene dosage or other post-transcriptional regulatory mechanisms, possibly through tissue specific expression of CNV-embedded small-noncoding RNAs (CNV-sncRNAs). Our objectives are to identify breast cancer associated CNVs using a genome wide association study (GWAS), identify sncRNA genes embedded within CNVs, confirm breast tissue (tumor and normal) expression of the sncRNAs, correlate their expression with germline copy status and identify pathways influenced by the genes regulated by sncRNAs. We used an association study design and accessed germline CNV data generated on Affymetrix Human SNP 6.0 array in 686 (in-house data) and 495 (TCGA data) subjects served as discovery and validation cohorts. We identified 1812 breast cancer associated CNVs harboring miRNAs (n = 38), piRNAs (n = 9865), snoRNAs (n = 71) and tRNAs (n = 12) genes. A subset of CNV-sncRNAs expressed in breast tissue, also showed correlation with germline copy status. We identified targets potentially regulated by miRNAs and snoRNAs. In summary, we demonstrate the potential impact of embedded CNV-sncRNAs on expression and regulation of down-stream targets.

Germline copy number variations are associated with breast cancer risk and prognosis

Breast cancer is one of the most common cancers among women, and susceptibility is explained by genetic, lifestyle and environmental components. Copy Number Variants (CNVs) are structural DNA variations that contribute to diverse phenotypes via gene-dosage effects or cis-regulation. In this study, we aimed to identify germline CNVs associated with breast cancer susceptibility and their relevance to prognosis. We performed whole genome CNV genotyping in 422 cases and 348 controls using Human Affymetrix SNP 6 array. Principal component analysis for population stratification revealed 84 outliers leaving 366 cases and 320 controls of Caucasian ancestry for association analysis; CNVs with frequency > 10% and overlapping with protein coding genes were considered for breast cancer risk and prognostic relevance. Coding genes within the CNVs identified were interrogated for gene- dosage effects by correlating copy number status with gene expression profiles in breast tumor tissue. We identified 200 CNVs associated with breast cancer (q-value < 0.05). Of these, 21 CNV regions (overlapping with 22 genes) also showed association with prognosis. We validated representative CNVs overlapping with APOBEC3B and GSTM1 genes using the TaqMan assay. Germline CNVs conferred dosage effects on gene expression in breast tissue. The candidate CNVs identified in this study warrant independent replication.

Runx3 in Immunity, Inflammation and Cancer

In this chapter we summarize the pros and cons of the notion that Runx3 is a major tumor suppressor gene (TSG). Inactivation of TSGs in normal cells provides a viability/growth advantage that contributes cell-autonomously to cancer. More than a decade ago it was suggested that RUNX3 is involved in gastric cancer development, a postulate extended later to other epithelial cancers portraying RUNX3 as a major TSG. However, evidence that Runx3 is not expressed in normal gastric and other epithelia has challenged the RUNX3-TSG paradigm. In contrast, RUNX3 is overexpressed in a significant fraction of tumor cells in various human epithelial cancers and its overexpression in pancreatic cancer cells promotes their migration, anchorage-independent growth and metastatic potential. Moreover, recent high-throughput quantitative genome-wide studies on thousands of human samples of various tumors and new investigations of the role of Runx3 in mouse cancer models have unequivocally demonstrated that RUNX3 is not a bona fide cell-autonomous TSG. Importantly, accumulating data demonstrated that RUNX3 functions in control of immunity and inflammation, thereby indirectly influencing epithelial tumor development.

A genome-wide association study identifies WT1 variant with better response to 5-fluorouracil, pirarubicin and cyclophosphamide neoadjuvant chemotherapy in breast cancer patients

Breast cancer is believed to result from the interplay of genetic and non-genetic risk factors, and individual genetic variation may influence the efficacy of chemotherapy. Here we conducted a genome-wide association study to identify single nucleotide polymorphisms (SNPs) associated with response to anthracycline- and taxane-based neoadjuvant chemotherapy in breast cancer patients. In the discovery stage, we divided 92 patients who received anthracycline-based neoadjuvant chemotherapy into 2 groups according to pathologic response and performed a genome-wide study using Affymetrix SNP6.0 genechip. Of 389,795 SNPs associated with pathologic complete response (pCR), we identified 2 SNPs, rs6044100 and rs1799937, that were significantly associated with pCR after neoadjuvant chemotherapy. In the validation stage, genotype analysis of samples from an independent cohort of 401 patients who received anthracycline-based neoadjuvant regimens and 467 patients who received taxane-based regimens was performed using sequencing analysis. We found that only SNP rs1799937, located in the WT1 gene, was associated with pCR after anthracycline-based neoadjuvant therapy (AA vs GG; odds ratio [OR], 2.81; 95% confidence interval [CI], 1.13-6.98; P < 0.05) but not after taxane-based neoadjuvant therapy (AA vs GG; OR, 0.85; 95% CI, 0.36-2.04; P = 0.72). These results suggest that WT1 may be a potential target of anthracycline-based neoadjuvant therapy for breast cancer.

A Genome-Wide Association Study to Identify Potential Germline Copy Number Variants for Sporadic Breast Cancer Susceptibility

Breast cancer (BC) predisposition in populations arises from both genetic and nongenetic risk factors. Structural variations such as copy number variations (CNVs) are heritable determinants for disease susceptibility. The primary objectives of this study are (1) to identify CNVs associated with sporadic BC using a genome-wide association study (GWAS) design; (2) to utilize 2 distinct CNV calling algorithms to identify concordant CNVs as a strategy to reduce false positive associations in the hypothesis-generating GWAS discovery phase, and (3) to identify potential candidate CNVs for follow-up replication studies. We used Affymetrix SNP Array 6.0 data profiled on Caucasian subjects (422 cases/348 controls) to call CNVs using algorithms implemented in Nexus Copy Number and Partek Genomics Suite software. Nexus algorithm identified CNVs associated with BC (731 autosomal CNVs with >5% frequency in the total sample and Q < 0.05). Thirteen CNVs were identified when Partek algorithm-called CNVs were overlapped with Nexus-identified CNVs; these CNVs showed concordances for frequency, effect size, and direction. Coding genes present within BC-associated CNVs were known to play a role in disease etiology and prognosis. Long noncoding RNAs identified within CNVs showed tissue-specific expression, indicating potential functional relevance of the findings. The identified candidate CNVs warrant independent replication.

Heterogeneity of Breast Cancer Associations with Common Genetic Variants in FGFR2 according to the Intrinsic Subtypes in Southern Han Chinese Women

GWAS have identified variation in the FGFR2 locus as risk factors for breast cancer. Validation studies, however, have shown inconsistent results by ethnics and pathological characteristics. To further explore this inconsistency and investigate the associations of FGFR2 variants with breast cancer according to intrinsic subtype (Luminal-A, Luminal-B, ER-&PR-&HER2+, and triple negative) among Southern Han Chinese women, we genotyped rs1078806, rs1219648, rs2420946, rs2981579, and rs2981582 polymorphisms in 609 patients and 882 controls. Significant associations with breast cancer risk were observed for rs2420946, rs2981579, and rs2981582 with OR (95% CI) per risk allele of 1.19 (1.03-1.39), 1.24 (1.07-1.43), and 1.17 (1.01-1.36), respectively. In subtype specific analysis, above three SNPs were significantly associated with increased Luminal-A risk in a dose-dependent manner (P trend < 0.01); however, only rs2981579 was associated with Luminal-B, and none were linked to ER-&PR- subtypes (ER-&PR-&HER2+ and triple negative). Haplotype analyses also identified common haplotypes significantly associated with luminal-like subtypes (Luminal-A and Luminal-B), but not with ER-&PR- subtypes. Our results suggest that associations of FGFR2 SNPs with breast cancer were heterogeneous according to intrinsic subtype. Future studies stratifying patients by their intrinsic subtypes will provide new insights into the complex genetic mechanisms underlying breast cancer.

Runx3 at the interface of immunity, inflammation and cancer

Inactivation of tumor suppressor genes (TSG) in normal cells provides a viability/growth advantage that contributes cell-autonomously to cancer. More than a decade ago claims arose that the RUNX3 member of the RUNX transcription factor family is a major TSG inactivated in gastric cancer, a postulate extended later to other cancers. However, evidence that Runx3 is not expressed in normal gastric and other epithelia has challenged the RUNX3-TSG paradigm. Here we critically re-appraise this paradigm in light of recent high-throughput, quantitative genome-wide studies on thousands of human samples of various tumors and new investigations of the role of Runx3 in mouse cancer models. Collectively, these studies unequivocally demonstrate that RUNX3 is not a bona fide cell-autonomous TSG. Accordingly, RUNX3 is not recognized as a TSG and is not included among the 2000 cancer genes listed in the "Cancer Gene Census" or "Network for Cancer Genes" repositories. In contrast, RUNX3 does play important functions in immunity and inflammation and may thereby indirectly influence epithelial tumor development.

Germline DNA variations in breast cancer predisposition and prognosis: a systematic review of the literature

Breast cancer is the most common cancer and the second leading cause of death in women worldwide. The disease is caused by a combination of genetic, environmental, lifestyle, and reproductive risk factors. Linkage and family-based studies have identified many pathological germline mutations, which account for around 20% of the genetic risk of familial breast cancer. In recent years, single nucleotide polymorphism-based genetic association studies, especially genome-wide association studies (GWASs), have been very successful in uncovering low-penetrance common variants associated with breast cancer risk. These common variants alone may explain up to an additional 30% of the familial risk of breast cancer. With the advent of available genetic resources and growing collaborations among researchers across the globe, the much needed large sample size to capture variants with small effect sizes and low population frequencies is being addressed, and hence many more common variants are expected to be discovered in the coming days. Here, major GWASs conducted for breast cancer predisposition and prognosis until 2013 are summarized. Few studies investigating other forms of genetic variations contributing to breast cancer predisposition and disease outcomes are also discussed. Finally, the potential utility of the GWAS-identified variants in disease risk models and some future perspectives are presented.

Polymorphisms in ESR1 and FLJ43663 are associated with breast cancer risk in the Han population

Breast cancer is a heterogeneous disease which is influenced by genetic, environmental, and lifestyle factors. Genetic susceptibility is likely to be due to variants conferring more moderate risks. To identify susceptibility alleles, we conducted a case-control association study in 185 breast cancer cases and 199 controls in the Han population. We genotyped 14 tagging single nucleotide polymorphisms previously implicated in breast cancer using Sequenom MassARRAY SNP genotyping method and identified rs3734805 in the ESR1 gene and rs2048672 in the FLJ43663 gene were associated with breast cancer risk. Allele "C" of rs3734805 was associated with increased breast cancer progression by χ (2) test and additive model analysis (OR = 1.36; 95% CI, 1.01-1.82; p = 0.042). Using recessive model analysis, we found that genotype "GG" of rs2048672 was the protective genotype during breast cancer progression (OR = 0.55; 95% CI, 0.32-0.95; p = 0.029). Our results provide additional insights into the opposing roles of the ESR1 and FLJ43663 genes in breast cancer onset and progression.