Abstract 2787: Exon sequencing of candidate genes for early onset ER negative breast cancer risk reveals novel gene-level associations
Authors: Scannell Bryan Molly , Kibirya Muhammad G. , Andrulis Irene , Chang-Claude Jenny , Ahsan Habibul , Pierce Brandon 
Published: August 2015

Abstract
Purpose: To test whether genes located in GWAS-identified regions contain exonic variants that show novel gene-level associations with early-onset ER negative breast cancer risk.
Background: Only a small portion of the expected genetic contribution to breast cancer risk has been identified by examining the effect of common variants using single-variant analyses. In contrast to single-variant analyses, sequencing studies combined with gene-based tests evaluate the collective effect of all variants in a gene. In regions identified as associated with disease in GWAS, sequencing combined with gene-based tests can potentially provide evidence whether exonic variation contributes to disease risk independently of the common variants already. However, these studies have not yet been widely implemented in breast cancer research.
Methods: We selected 19 genes in 11 genomic regions in which previous GWA studies found associations between common variants and breast cancer. We sequenced the exons of each of these genes in 210 cases (women diagnosed with breast cancer before age 45 who did not carry a known BRCA-1 or BRCA-2 mutation and whose tumors were ER-), and 169 age-matched controls. We analyzed these exons using the variance-based SKAT-O test to determine if exonic variation in any of these 19 genes was associated with risk of developing breast cancer. To examine whether any association was driven by the known GWAS variant, we repeated the analysis, controlling for the common variant that single-variant association tests indicated was most strongly associated with breast cancer. To examine whether the association was driven by putative “functional” variants, we also repeated both analyses, including only non-synonymous variants that alter the amino acid sequence.
Results: Exonic variants in three genes were collectively associated with breast cancer risk in our population of early-onset cases: ZMIZ1 (p = 2.07•10-4), FGF3 (p = 1.30•10-3), and ANKLE1 (p = 2.80•10-5). In all of these three genes, the associations persisted or even strengthened after adjusting for the top variant identified by GWAS in the region (ZMIZ1 p = 2.41•10-5; FGF3 p = 1.41•10-3; ANKLE1 p = 7.63•10-6). Functional variants in these three genes (restricted only to non-synonomous variants) also were collectively associated with risk (ZMIZ1 p = 2.65•10-5; FGF3 p = 4.52•10-5; ANKLE1 p = 6.52•10-5). These associations are similar after adjusting for the strongest single variant association identified by GWAS in the region (ZMIZ1 p = 5.10•10-4; FGF3 p = 7.74•10-5; ANKLE1 p = 9.42•10-5).
Conclusions: Our results are consistent with the hypothesis that the exons of genomic regions identified through GWAS contain additional variants that contribute to ER- breast cancer risk. These results, that need to be independently validated in a larger study, contribute to our understanding of the genetic determinants that influence the risk of ER- early onset breast cancer.
Citation Format: Molly Scannell Bryan, Muhammad G. Kibirya, Irene Andrulis, Jenny Chang-Claude, Habibul Ahsan, Brandon Pierce. Exon sequencing of candidate genes for early onset ER negative breast cancer risk reveals novel gene-level associations. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2787. doi:10.1158/1538-7445.AM2015-2787