rs3734805

A hospital-based case-control study in rural and urban India (1,204 cases; 1,212 controls) examined genetic and lifestyle risk factors for breast cancer. Four SNPs in FGFR2 (rs1219648, rs2420946, rs2981575, rs2981582) showed positive associations with breast cancer (ORs 1.32-1.47). Additional SNPs in obesity and metabolic genes (rs374748 in FBN2, rs2922763 in HNF4G, rs2116830 in KCNMA1, rs11121832 in MTHFR, rs16886165 in MAP3K1, rs11594610 in TCF7L2, rs2274459 in MLN) were associated with increased breast cancer risk. Waist-to-hip ratio ≥0.95 showed strong association (OR 3.78; 95% CI 2.92-4.89), and women living first 20 years in rural areas showed protective effect (OR 0.77).

This multi-stage genome-wide association study in 11,705 BRCA1 mutation carriers identified three novel cancer risk-modifying loci: rs2290854 at 1q32 associated with breast cancer (HR=1.14), and rs17631303 (HR=1.27) and rs4691139 (HR=1.20) at 17q21.31 and 4q32.3 respectively associated with ovarian cancer. The 4q32.3 locus showed BRCA1-specific associations. These findings enable improved absolute risk estimation for BRCA1 carriers, with estimated breast cancer lifetime risks ranging from 28-50% for the lowest-risk 5% to 81-100% for the highest-risk 5%.