Purpose
Genome-wide association studies (GWAS) have identified dozens of single nucleotide polymorphisms (SNPs) associated with breast cancer. Few studies focused on young-onset breast cancer, which exhibits etiologic and tumor-type differences from older-onset disease. Possible confounding by prenatal effects of the maternal genome has also not been considered.
Methods
Using a family-based design for breast cancer before age 50, we assessed the relationship between breast cancer and 77 GWAS-identified breast cancer risk SNPs. We estimated relative risks (RR) for inherited and maternally-mediated genetic effects. We also used published RR estimates to calculate genetic risk scores and model joint effects.
Results
Seventeen of the candidate SNPs were nominally associated with young-onset breast cancer in our 1,296 non-Hispanic white affected families (uncorrected p-value<0.05). Top-ranked SNPs included rs3803662-A (TOX3, RR=1.39; p=7.0×10−6), rs12662670-G (ESR1, RR=1.56; p=5.7×10−4), rs2981579-A (FGFR2, RR=1.24; p=0.002), and rs999737-G (RAD51B, RR=1.37; p=0.003). No maternally-mediated effects were found. A risk score based on all 77 SNPs indicated that their overall relationship to young-onset breast cancer risk was more than additive (additive-fit p=2.2×10−7) and consistent with a multiplicative joint effect (multiplicative-fit p=0.27). With the multiplicative formulation, the case sister’s genetic risk score exceeded that of her unaffected sister in 59% of families.
Conclusions
The results of this family-based study indicate that no effects of previously-identified risk SNPs were explained by prenatal effects of maternal variants. Many of the known breast cancer risk variants were associated with young-onset breast cancer, with evidence that TOX3, ESR1, FGFR2, and RAD51B are important for young-onset disease.