Most breast cancer heritability is unexplained. We hypothesized that analysis of unrelated familial cases in a GWAS context could enable the identification of novel susceptibility loci. In order to examine the association of a haplotype with breast cancer risk, we performed a genome-wide haplotype association study using a sliding window analysis of window sizes 1-25 SNPs in 650 familial invasive breast cancer cases and 5021 controls. We identified five novel risk loci on 9p24.3 (OR 3.4; p 4.9 × 10-11), 11q22.3 (OR 2.4; p 5.2 × 10-9), 15q11.2 (OR 3.6; p 2.3 × 10-8), 16q24.1 (OR 3; p 3 × 10-8) and Xq21.31 (OR 3.3; p 1.7 × 10-8) and confirmed three well-known loci on 10q25.13, 11q13.3, and 16q12.1. In total, 1593 significant risk haplotypes and 39 risk SNPs were distributed on the eight loci. In comparison with unselected breast cancer cases from a previous study, the OR was increased in the familial analysis in all eight loci. Analyzing familial cancer cases and controls enabled the identification of novel breast cancer susceptibility loci.
Keywords: GRIA4; GWAS; SMARCA2; TGIF2LX; breast cancer; familial; haplotype; risk loci.