Prevalence of BRCA1 and BRCA2 mutations in Ashkenazi Jewish families with breast and pancreatic cancer.

BACKGROUND: Germline mutations in the BRCA2 cancer susceptibility gene are associated with an increased risk of pancreatic cancer (PC). Breast-pancreas cancer families with BRCA1 mutations have also been observed. The influence of a family history (FH) of PC on BRCA mutation prevalence in patients with breast cancer (BC) is unknown. METHODS: A clinical database review (2000-2009) identified 211 Ashkenazi Jewish (AJ) BC probands who 1) underwent BRCA1/2 mutation analysis by full gene sequencing or directed testing for Ashkenazi founder mutations (BRCA1: 185delAG and 5382insC; BRCA2: 6174delT) and 2) had a FH of PC in a first-, second-, or third-degree relative. For each proband, the pretest probability of identifying a BRCA1/2 mutation was estimated using the Myriad II model. The observed-to-expected (O:E) mutation prevalence was calculated for the entire group. RESULTS: Of the 211 AJ BC probands with a FH of PC, 30 (14.2%) harbored a BRCA mutation. Fourteen (47%) of the mutations were in BRCA1 and 16 (53%) were in BRCA2. Patients diagnosed with BC at age ≤ 50 years were found to have a higher BRCA1/2 mutation prevalence than probands with BC who were diagnosed at age > 50 years (21.1% vs 6.9%; P = .003). In patients with a first-, second-, or third-degree relative with PC, mutation prevalences were 15.4%, 15.3%, and 8.6%, respectively (P = .58). In the overall group, the observed BRCA1/2 mutation prevalence was 14.2% versus an expected prevalence of 11.8% (O:E ratio, 1.21; P = .15). CONCLUSIONS: BRCA1 and BRCA2 mutations are observed with nearly equal distribution in AJ breast-pancreas cancer families, suggesting that both genes are associated with PC risk. In this population, a FH of PC was found to have a limited effect on mutation prevalence.

Genome-wide association studies of cancer predisposition.

Genome-wide association studies (GWAS) have now been performed in nearly all common malignancies and have identified more than 100 common genetic risk variants that confer a modest increased risk of cancer. For most discovered germline risk variants, the per allele effect size is small (<1.5) and the biologic mechanism of the detected association remains unexplained. Exceptions are the risk variants identified in JAK2 in myeloproliferative neoplasm and in the KITLG gene in testicular cancer, which are each associated with nearly a 3-fold increased risk of disease. GWAS have provided an efficient approach to identifying common, low-penetrance risk variants, and have implicated several novel cancer susceptibility loci. However, the identified low-penetrance risk variants explain only a small fraction of the heritability of cancer and the clinical usefulness of using these variants for cancer-risk prediction is to date limited. Studies involving more heterogeneous populations, determination of the causal variants, and functional studies are now necessary to further elucidate the potential biologic and clinical significance of the observed associations.

Absence of genomic BRCA1 and BRCA2 rearrangements in Ashkenazi breast and ovarian cancer families.

A substantial proportion of Ashkenazi Jewish (AJ) breast and ovarian cancer families carry one of three founder mutations in BRCA1 (185delAG, 5382InsC) and BRCA2 (6174delT). Non-founder mutations are identified in another 2-4% of such families. The extent to which major genomic rearrangements in BRCA contribute to breast and ovarian cancer in the Ashkenazim is not well understood. We identified AJ individuals with breast and/or ovarian cancer undergoing hereditary breast/ovarian cancer risk assessment since 2006 without evidence of a deleterious mutation on BRCA gene sequencing who were screened for major gene rearrangements in BRCA1 and BRCA2. For each proband, the pre-test probability of identifying a deleterious BRCA mutation was estimated using the Myriad II model. We identified 108 affected individuals who underwent large rearrangement testing (80 breast cancer, 19 ovarian cancer, nine both breast and ovarian cancer). The mean estimated AJ specific pre-test probability of a deleterious mutation in BRCA1 and BRCA2 was 24.7% (range: 4.4-88.9%). No genomic rearrangements were identified in either the entire group or in the 26 subjects with pre-test mutation prevalence estimates exceeding 30%. Major gene rearrangements involving the BRCA1 and BRCA2 genes appear to contribute little to the burden of inherited predisposition to breast and ovarian cancer in the Ashkenazim.