Proffered Papers and Posters Submitted to the Fifth International Symposium on Hereditary Breast and Ovarian Cancer, BRCA: Twenty Years of Advances ^†

Objectives: It is estimated that 1–2% of individuals of Ashkenazi Jewish (AJ) ancestry carry one of three pathogenic founder mutations in BRCA1 and BRCA2. Targeted testing for these mutations (BRCA1 187delAG and 5385insC, and BRCA2 6174delT) is therefore recommended for all AJ breast and ovarian cancer patients, regardless of age of diagnosis or family history. Comprehensive analysis of both genes is recommended for a subset of AJ patients in whom founder mutations are not identified, but estimates of the yield from comprehensive analysis in this population vary widely. Methods: We sought to establish the proportion of non-founder mutations in AJ patients undergoing clinical testing in our laboratory from January 2006 through August 2013. Analysis included AJ patients for whom: (1) comprehensive testing was ordered as the initial test, or (2) founder mutation testing was ordered with instructions to “reflex” to comprehensive analysis if negative. The latter group was limited to cases where the reflex testing was ordered on the original test request form, and not cancelled for any reason other than the detection of a founder mutation. Results: The percentage of non-founder mutations detected in these groups was 13% (104/802) and 7.2% (198/2769) respectively. We detected 189 unique non-founder mutations, 76 in BRCA1 and 113 in BRCA2. BRCA2 4075delGT was detected in 15 patients. The next most common mutations, found in 7 patients each, were BRCA1 5055delG, BRCA2 1982delA, and BRCA2 R3128X. Conclusions: Non-founder mutations make up between 13% and 7.2% of BRCA1 and BRCA2 mutations in patients reporting AJ ancestry. These numbers may represent underestimates if some patients were ascertained for testing based on the identification of a founder mutation in a relative. These numbers suggest that the prevalence of non-founder mutations in AJ individuals may be comparable to the prevalence of BRCA1/2 mutations in non-AJ individuals.