Incidence of Breast Cancer and Its Subtypes in Relation to Individual and Multiple Low-Penetrance Genetic Susceptibility Loci

CONTEXT There is limited evidence on how the risk of breast cancer and its subtypes depend on low-penetrance susceptibility loci, individually or in combination. OBJECTIVE To analyze breast cancer risk, overall and by tumor subtype, in relation to 14 individual single-nucleotide polymorphisms (SNPs) previously linked to the disease, and in relation to a polygenic risk score. DESIGN, SETTING, AND PARTICIPANTS Study of 10 306 women with breast cancer (mean age at diagnosis, 58 years) and 10 393 women without breast cancer who in 2005-2008 provided blood samples for genotyping in a large prospective study of UK women; and meta-analysis of these results and of other published results. MAIN OUTCOME MEASURES Estimated per-allele odds ratio (OR) for individual SNPs, and cumulative incidence of breast cancer to age 70 years in relation to a polygenic risk score based on the 4, 7, or 10 SNPs most strongly associated with risk. RESULTS Odds ratios for breast cancer were greatest for FGFR2-rs2981582 and TNRC9-rs3803662 and, for these 2 SNPs, were significantly greater for estrogen receptor (ER)–positive than for ER-negative disease, both in our data and in meta-analyses of all published data (pooled per-allele ORs [95% confidence intervals] for ER-positive vs ER-negative disease: 1.30 [1.26-1.33] vs 1.05 [1.01-1.10] for FGFR2; interaction P