IntroductionBreast cancer is a heterogeneous disease, and the distribution of the different subtypes varies by race/ethnic category in the United States and by country. Established breast cancer-associated factors impact subtype-specific risk; however, these included limited or no representation of Latin American diversity. To address this gap in knowledge, we report a description of demographic, reproductive, and lifestyle breast cancer-associated factors by age at diagnosis and disease subtype for The Peruvian Genetics and Genomics of Breast Cancer (PEGEN-BC) study.MethodsThe PEGEN-BC study is a hospital-based breast cancer cohort that includes 1943 patients diagnosed at the Instituto Nacional de Enfermedades Neoplásicas in Lima, Peru. Demographic and reproductive information, as well as lifestyle exposures, were collected with a questionnaire. Clinical data, including tumor Hormone Receptor (HR) status and Human Epidermal Growth Factor Receptor 2 (HER2) status, were abstracted from electronic medical records. Differences in proportions and mean values were tested using Chi-squared and one-way ANOVA tests, respectively. Multinomial logistic regression models were used for multivariate association analyses.ResultsThe distribution of subtypes was 52% HR+HER2-, 19% HR+HER2+, 16% HR-HER2-, and 13% HR-HER2+. Indigenous American (IA) genetic ancestry was higher, and height was lower among individuals with the HR-HER2+ subtype (80% IA vs. 76% overall, p=0.007; 152 cm vs. 153 cm overall, p=0.032, respectively). In multivariate models, IA ancestry was associated with HR-HER2+ subtype (OR=1.38,95%CI=1.06-1.79, p=0.017) and parous women showed increased risk for HR-HER2+ (OR=2.7,95%CI=1.5-4.8, p<0.001) and HR-HER2- tumors (OR=2.4,95%CI=1.5-4.0, p<0.001) compared to nulliparous women. Multiple patient and tumor characteristics differed by age at diagnosis (<50 vs. >=50), including ancestry, region of residence, family history, height, BMI, breastfeeding, parity, and stage at diagnosis (p<0.02 for all variables).DiscussionThe characteristics of the PEGEN-BC study participants do not suggest heterogeneity by tumor subtype except for IA genetic ancestry proportion, which has been previously reported. Differences by age at diagnosis were apparent and concordant with what is known about pre- and post-menopausal-specific disease risk factors. Additional studies in Peru should be developed to further understand the main contributors to the specific age of onset and molecular disease subtypes in this population and develop population-appropriate predictive models for prevention.

Background: Breast cancer incidence in the United States is lower in Hispanic/Latina (H/L) compared with African American/Black or Non-Hispanic White women. An Indigenous American breast cancer–protective germline variant (rs140068132) has been reported near the estrogen receptor 1 gene. This study tests the association of rs140068132 and other polymorphisms in the 6q25 region with subtype-specific breast cancer risk in H/Ls of high Indigenous American ancestry. Methods: Genotypes were obtained for 5,094 Peruvian women with (1,755) and without (3,337) breast cancer. Associations between genotype and overall and subtype-specific risk for the protective variant were tested using logistic regression models and conditional analyses, including other risk-associated polymorphisms in the region. Results: We replicated the reported association between rs140068132 and breast cancer risk overall [odds ratio (OR), 0.53; 95% confidence interval (CI), 0.47–0.59], as well as the lower odds of developing hormone receptor negative (HR−) versus HR+ disease (OR, 0.77; 95% CI, 0.61–0.97). Models, including HER2, showed further heterogeneity with reduced odds for HR+HER2+ (OR, 0.68; 95% CI, 0.51–0.92), HR−HER2+ (OR, 0.63; 95% CI, 0.44–0.90) and HR−HER2− (OR, 0.77; 95% CI, 0.56–1.05) compared with HR+HER2−. Inclusion of other risk-associated variants did not change these observations. Conclusions: The rs140068132 polymorphism is associated with decreased risk of breast cancer in Peruvians and is more protective against HR− and HER2+ diseases independently of other breast cancer-associated variants in the 6q25 region. Impact: These results could inform functional analyses to understand the mechanism by which rs140068132-G reduces risk of breast cancer development in a subtype-specific manner. They also illustrate the importance of including diverse individuals in genetic studies.

Breast cancer subtype distribution differs between populations with dissimilar genetic ancestry backgrounds. Several breast cancer risk single nucleotide polymorphisms (SNPs) were discovered in individuals of European and Asian origin. Hispanic/Latina women remain underrepresented in studies and public databases. The 6q25 locus contains multiple breast cancer risk-associated SNPs. Some SNPs within this region have been associated with the expression of genes (eQTLs), such as the Estrogen Receptor 1 gene (ESR1). Two breast cancer genetic association studies in Hispanics/Latinas identified two SNPs (rs140068132 and rs3778609), near ESR1, that correlate with Indigenous American ancestry and reduce the odds of breast cancer, especially for Estrogen Receptor-negative (ER-) disease. The underrepresentation of Latin American populations in public databases has hindered the study of the mechanisms by which these SNPs confer a protective effect. We integrated genetic and transcriptomic data from breast cancer patients with high Indigenous American ancestry to test the association between the protective variants in the 6q25 region and tumor gene expression. Breast cancer patients were recruited at the National Cancer Institute in Peru to be part of The Peruvian Genetics and Genomics of Breast Cancer Study (PEGEN-BC, N=1809). Healthy women from a pregnancy outcomes study in Peru were included as controls (N=3334). Genome-wide genotype data were available and missing genotypes were imputed using the TOPMED Imputation Server to perform fine-mapping within the 6q25 locus. Logistic regression was used to test the association between each SNP and breast cancer risk. We exome-sequenced 155 breast tumors of these patients. Transcripts per million counts and imputed genotypes within the 6q25 region were used for eQTL analysis. Colocalization was performed using summary statistics from the fine-mapping and eQTL analysis, including SNPs with minor allele frequency >5%. Only two SNPs, rs140068132 and rs851984 were independently associated with breast cancer risk, as we previously reported. eQTL signals colocalized with the subregion in 6q25 that contains these breast cancer-associated SNPs. Within this subregion, the gene with more eQTLs using a nominal p-value of <=0.01 was MTHFD1L (136 eQTLs), followed by ESR1 (58) and CCDC170 (32). Colocalization showed that MTHFD1L and ESR1 eQTLs were more likely to overlap with breast cancer risk SNPs, including rs140068132. The protective rs140068132-G variant was associated with lower expression of MTHFD1L. MTHFD1L has been found deregulated in breast cancer and higher expression is associated with poor prognosis. Our preliminary results suggest that the rs140068132-G variant in the 6q25 region identified in Hispanic/Latina women might exert its protective effect through the downregulation of MTHFD1L. Analyses with additional samples will allow us to confirm this result and further explore the functional implications of the rs140068132 variant. Citation Format: Valentina A. Zavala, Xiaosong Huang, Sandro Casavilca-Zambrano, Jeannie Navarro-Vásquez, Carlos A. Castañeda, Guillermo Valencia, Zaida Morante, Monica Calderon, Julio E. Abugattas, Henry Gómez, Hugo A. Fuentes, Ruddy Liendo-Picoaga, Jose M. Cotrina, Silvia Neciosup, Katia Roque, Jule Vásquez, Luis MAs, Marco Gálvez-Nino, Sixto E. Sánchez, Michelle A. Williams, Elad Ziv, Jovanny Zabaleta, Bizu Gelaye, Tatiana Vidaurre Vidaurre, Laura Fejerman. Breast cancer risk in Hispanic/Latina women and the 6q25 chromosomal region: Fine mapping and eQTL identification [abstract]. In: Proceedings of the 15th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2022 Sep 16-19; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2022;31(1 Suppl):Abstract nr C082.

The incidence of Human Epidermal Growth Factor Receptor 2 positive (HER2+) breast cancer is higher in Latinas, both in the U.S. and in Latin America. Preliminary analyses of the Peruvian Genetics and Genomics of Breast Cancer (PEGEN-BC) study data set showed a strong association between the Indigenous American (IA) component of ancestry and HER2 status independently of stage at diagnosis and other factors. The aim of this study was to identify genetic loci associated with genetic ancestry and HER2+ breast cancer in patients with high IA ancestry. To achieve this aim we used admixture mapping and gene-expression guided fine mapping. Breast cancer patients were recruited at the Instituto Nacional de Enfermedades Neoplásicas in Lima, Peru. A total of 1,850 patients have been recruited to date. DNA samples are currently available for a total of 1,380 patients. Genome wide genotypes were obtained with the Affymetrix Precision Medicine Research Array. After quality control, genome wide genotype data was available for 1,312 patients. After LD pruning and exclusion of SNPs with minor allele frequency <0.05, we estimated global ancestry with the program ADMIXTURE and locus-specific ancestry using RFMix. Tumor subtypes were classified using immunohistochemistry markers for estrogen, progesterone and HER2 receptors. Admixture mapping was conducted using logistic regression models. The outcome variable was HER2 status (HER2+ =1, HER2- =0). Global Individual IA ancestry and age at diagnosis were included as covariates. For transcriptomic analysis within regions of interest we used exome sequencing data (Illumina NextSeq500 system) for total RNA extracted from 79 FFPE tumor tissues from the same cohort. Genes within regions with suggestive admixture mapping signals were further analyzed by comparing normalized RNA read counts by HER2+ status using the DEseq2 R package. Admixture mapping analysis revealed two regions associated with IA ancestry in two chromosomal regions: 2q11-2q12 (OR=0.6, p=0.00009) and 3p14 (OR=1.5, p= 0.0004). Of the 44 genes within the 2q region, TGFBRAP1, member of the heat shock protein 90 family, was the only gene with suggestive differential expression by HER2 status (p=0.032). Of the 28 genes within the 3p14 region, we found significant differential expression for FLNB (lower expression in HER2+ tumours, 5%FDR= 0.03), which has been shown to supress tumour growth and metastasis. Combining admixture mapping and transcriptomics is a promising approach to discover candidate genes associated with subtype-specific breast cancer risk. We are currently working to replicate suggestive findings and expand our sample size to increase power. Citation Format: Valentina Zavala, Katie M. Marker, Tatiana Vidaurre, Jeannie Navarro-Vasquez, Sandro Casavilca, Mónica Calderon, Julio Abugattas, Henry Gómez, Hugo Fuentes, Ruddy Liendo-Picoaga, Jose M. Cotrina, Silvia P. Neciosup, Carlos A. Castaneda, Zaida Morante, Fernando Valencia, Silvia J. Serrano-Gomez, Jovanny Zabaleta, Laura Fejerman. Admixture mapping and gene expression analysis to identify candidate genes associated with HER2 positive breast cancer in Latinas [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4615.

Genetic studies in women of Hispanic/Latina origin identified a single nucleotide polymorphism (SNP) in the 6q25 region, rs140068132, that correlates with Indigenous American (IA) ancestry and is protective against BC. The underrepresentation of Latin American populations in public databases has hindered the study of the mechanisms by which this SNP confers a protective effect. We aimed to identify IA germline variants associated with BC risk and to test their association with tumor gene expression in this region. We performed a case-control fine-mapping analysis in the 6q25 region. BC patients part of the PEGEN-BC Study (N=1809) were included as cases and women from a pregnancy outcomes study in Peru as controls (N=3334). Genome-wide genotype data were available and missing genotypes were imputed using the TOPMED Imputation Server. Logistic regression was used to test the association between each SNP and BC risk. We exome-sequenced 247 breast tumors of PEGEN-BC patients. Tumor subtype was assigned by the pam50 method. We excluded patients diagnosed with stage IV disease, with tumors classified as normal-like or as uncertain, and carriers of the GG genotype for rs140068132, leaving 242 samples. Association between rs140068132 and gene expression of genes in the 6q25 region was tested adjusting by age at diagnosis and IA ancestry. The strongest signal corresponded to rs140068132 (odds ratio (OR)=0.53, p=1.9e-21). The model adjusted by rs140068132 revealed three additional independent variants that correlate with Indigenous American ancestry: rs184135739 (OR=0.8, p=0.006), rs141057867 (OR=0.87, p=0.006) and rs140125124 (OR=1.23, p=0.015). Gene expression analysis stratified by subtype revealed that among HER2+ tumors (N=63), rs140068132 was associated with ARMT1 (fold change comparing AA to AG (FC)=1.6, p<0.01), CCDC170 (FC=1.8, p<0.01), MTHFD1L (FC=0.7, p<0.01) and RMND1 (FC=1.4, p=0.013). Among Luminal-B (N=68) tumors, there was an association with ARMT1 (FC= 1.9, p=0.001), ESR1 (FC=1.4, p=0.04) and MTHFD1L (FC= 0.8, p=0.02). Only ESR1 was associated with the SNP (FC= 0.5, p= 0.03) among basal tumors (N=56). No association was identified among Luminal-A tumors (N=55). rs141057867 showed evidence of cis-association with CLDN20 (FC=1.4, p=0.014) among HER2+ subtypes and rs184135739 with ZC3H12D (FC=2.1, p=0.02) and SUMO4 (FC=1.8, p=0.023) among Lumina-A tumors. Two of the three novel IA SNPs are protective against BC and show association with gene expression. The rs140068132-G variant regulates the expression of genes in the 6q25 region in a subtype-specific manner. A possible mechanism explaining the protective effect of the rs140068132 polymorphism might be linked to the lower expression of MTHFD1L among G-allele carriers in some subtypes. This gene is deregulated in cancer and its expression is negatively associated with cancer survival, including BC. Citation Format: Valentina A. Zavala, Xiaosong Huang, Sandro Casavilca-Zambrano, Jeannie Navarro-Vásquez, Carlos A. Castañeda, Guillermo Valencia, Zaida Morante, Monica Calderon, Julio E. Abugattas, Henry Gómez, Hugo Fuentes, Ruddy Liendo-Picoaga, Jose M. Cotrina, Katia Roque, Jule Vásquez, Luis Mas, Marco Gálvez-Nino, Jovanny Zabaleta, Tatiana Vidaurre, Laura Fejerman. Regulation of genes located in 6q25 by an Indigenous American genetic variant in breast cancer patients from Peru. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5237.