Background: Recent candidate and genome wide association studies have identified variants altering susceptibility to breast cancer. We aimed to establish the relevance of these variants to breast cancer risk in familial breast cancer cases both with and without BRCA1 or BRCA2 (BRCA1/2) mutations.
Methods: A cohort of unrelated individuals affected from breast cancer due to the presence of either BRCA1 (121) or BRCA2 mutations (109) and females with familial breast cancer, not due to BRCA1/2 mutations (722) were genotyped using Taqman SNP Genotyping Assays. Allele frequencies were compared with an ethnically and gender-matched group (436).
Results: A synonymous variant (Ser51) in TOX3 (previously TNRC9) was associated with an increased risk of breast cancer (OR=p<0.001) in BRCA2 mutation carriers. We replicated the associations for FGFR2 (p=0.046), TOX3 (p<0.001), MAP3K1 (p=0.03), CASP8 (p=0.02) and the chromosome 8-associated SNP (p=0.004) in individuals without BRCA1/2 mutations. Additionally, homozygote carriers of MAP3K1 variants were shown to have a significantly lower Manchester Score (p=0.003), while individuals carrying one or two copies of the FGFR2 variant had a higher Manchester Score (p=0.01).
Conclusion: Our study confirms that susceptibility variants in FGFR2, TOX3, MAP3K1, and on chromosome 8q are all associated with increased risk of cancer in individuals with a family history of breast cancer, whereas CASP8 is protective in this context. The level of risk is dependent upon the strength of the family history and the presence of a BRCA1/2 mutation and contributes to the understanding of the use of these variants in clinical risk prediction.
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