Most common breast cancer susceptibility variants have been identified through genome-wide association studies (GWAS) of predominantly estrogen receptor (ER)-positive disease1. We conducted a GWAS using 21,468 ER-negative cases and 100,594 controls combined with 18,908 BRCA1 mutation carriers (9,414 with breast cancer), all of European origin. We identified independent associations at P < 5 × 10−8 with ten variants at nine new loci. At P < 0.05, we replicated associations with 10 of 11 variants previously reported in ER-negative disease or BRCA1 mutation carrier GWAS and observed consistent associations with ER-negative disease for 105 susceptibility variants identified by other studies. These 125 variants explain approximately 14% of the familial risk of this breast cancer subtype. There was high genetic correlation (0.72) between risk of ER-negative breast cancer and breast cancer risk for BRCA1 mutation carriers. These findings may lead to improved risk prediction and inform further fine-mapping and functional work to better understand the biological basis of ER-negative breast cancer.

The prevalence and spectrum of germline mutations in BRCA1 and BRCA2 have been reported in single populations, with the majority of reports focused on White in Europe and North America. The Consortium of Investigators of Modifiers of BRCA1/2 (CIMBA) has assembled data on 18,435 families with BRCA1 mutations and 11,351 families with BRCA2 mutations ascertained from 69 centers in 49 countries on six continents. This study comprehensively describes the characteristics of the 1,650 unique BRCA1 and 1,731 unique BRCA2 deleterious (disease‐associated) mutations identified in the CIMBA database. We observed substantial variation in mutation type and frequency by geographical region and race/ethnicity. In addition to known founder mutations, mutations of relatively high frequency were identified in specific racial/ethnic or geographic groups that may reflect founder mutations and which could be used in targeted (panel) first pass genotyping for specific populations. Knowledge of the population‐specific mutational spectrum in BRCA1 and BRCA2 could inform efficient strategies for genetic testing and may justify a more broad‐based oncogenetic testing in some populations.

A B S T R A C T PurposeImmunohistochemistry (IHC) for MLH1, MSH2, MSH6, and PMS2 protein expression and microsatellite instability (MSI) are well-established tools to screen for Lynch syndrome (LS). Although many cancer centers have adopted these tools as reflex LS screening after a colorectal cancer diagnosis, the standard of care has not been established, and no formal studies have described this practice in the United States. The purpose of this study was to describe prevalent practices regarding IHC/MSI reflex testing for LS in the United States and the subsequent follow-up of abnormal results. Materials and MethodsA 12-item survey was developed after interdisciplinary expert input. A letter of invitation, survey, and online-survey option were sent to a contact at each cancer program. A modified Dillman strategy was used to maximize the response rate. The sample included 39 National Cancer Institute-designated Comprehensive Cancer Centers (NCI-CCCs), 50 randomly selected American College of Surgeons-accredited Community Hospital Comprehensive Cancer Programs (COMPs), and 50 Community Hospital Cancer Programs (CHCPs). ResultsThe overall response rate was 50%. Seventy-one percent of NCI-CCCs, 36% of COMPs, and 15% of CHCPs were conducting reflex IHC/MSI for LS; 48% of the programs used IHC, 14% of the programs used MSI, and 38% of the programs used both IHC and MSI. One program used a presurgical information packet, four programs offered an opt-out option, and none of the programs required written consent. ConclusionAlthough most NCI-CCCs use reflex IHC/MSI to screen for LS, this practice is not well-adopted by community hospitals. These findings may indicate an emerging standard of care and diffusion from NCI-CCC to community cancer programs. Our findings also described an important trend away from requiring written patient consent for screening.