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BACKGROUNDGenetic testing for breast cancer susceptibility is widely used, but for many genes,evidence of an association with breast cancer is weak, underlying risk estimatesare imprecise, and reliable subtype-specific risk estimates are lacking.METHODSWe used a panel of 34 putative susceptibility genes to perform sequencing onsamples from 60,466 women with breast cancer and 53,461 controls. In separateanalyses for protein-truncating variants and rare missense variants in these genes,we estimated odds ratios for breast cancer overall and tumor subtypes. We evaluatedmissense-variant associations according to domain and classification of pathogenicity.RESULTSProtein-truncating variants in 5 genes (ATM, BRCA1, BRCA2, CHEK2, and PALB2)were associated with a risk of breast cancer overall with a P value of less than0.0001. Protein-truncating variants in 4 other genes (BARD1, RAD51C, RAD51D,and TP53) were associated with a risk of breast cancer overall with a P value ofless than 0.05 and a Bayesian false-discovery probability of less than 0.05. Forprotein-truncating variants in 19 of the remaining 25 genes, the upper limit ofthe 95% confidence interval of the odds ratio for breast cancer overall was lessthan 2.0. For protein-truncating variants in ATM and CHEK2, odds ratios werehigher for estrogen receptor (ER)–positive disease than for ER-negative disease;for protein-truncating variants in BARD1, BRCA1, BRCA2, PALB2, RAD51C, andRAD51D, odds ratios were higher for ER-negative disease than for ER-positivedisease. Rare missense variants (in aggregate) in ATM, CHEK2, and TP53 wereassociated with a risk of breast cancer overall with a P value of less than 0.001.For BRCA1, BRCA2, and TP53, missense variants (in aggregate) that would be classified as pathogenic according to standard criteria were associated with a riskof breast cancer overall, with the risk being similar to that of protein-truncatingvariants.CONCLUSIONSThe results of this study define the genes that are most clinically useful for inclusion on panels for the prediction of breast cancer risk, as well as provide estimatesof the risks associated with protein-truncating variants, to guide genetic counseling. (Funded by European Union Horizon 2020 programs and others.)

Ninety-four common genetic variants are confirmed to be associated with breast cancer. This study tested the hypothesis that breast cancer susceptibility variants may also be associated with chemotherapy-induced toxicity through shared mechanistic pathways such as DNA damage response, an association that, to our knowledge, has not been previously investigated. The study included breast cancer patients who received neoadjuvant/adjuvant chemotherapy from the Pharmacogenetic SNPs (PGSNPS) study. For each patient, a breast cancer polygenic risk score was created from the 94 breast cancer risk variants, all of which were genotyped or successfully imputed in PGSNPS. Logistic regression was performed to test the association with two clinically important toxicities: taxane- related neuropathy (n = 1279) and chemotherapy-induced neutropenia (n = 1676). This study was well powered (≥96%) to detect associations between polygenic risk score and chemotherapy toxicity. Patients with high breast cancer risk scores experienced less neutropenia compared to those with low risk scores (adjusted p-value = 0.06). Exploratory functional pathway analysis was performed and no functional pathways driving this trend were identified. Polygenic risk was not associated with taxane neuropathy (adjusted p-value = 0.48). These results suggest that breast cancer patients with high genetic risk of breast cancer, conferred by common variants, can safely receive standard chemotherapy without increased risk of taxane-related sensory neuropathy or chemotherapy-induced neutropenia and may experience less neutropenia. As neutropenia has previously been associated with improved survival and may reflect drug efficacy, these patients may be less likely to benefit from standard chemotherapy treatment.\ud \ud