Detection of germline deleterious mutations in prostate cancer patients with use of a validated 30-gene sequencing assay.

Abstract

223 Background: Germline DNA repair gene alterations in men with metastatic prostate cancer (PC) unselected for family history of malignancy occur in a greater frequency compared to localized PC and the general population. We hypothesized that assessing heritable alterations in a broader panel of high-susceptibility genes, may be relevant for detecting familial associations with other cancers in PC patients. Methods: We examined a cohort of 52 PC patients (median age 60, range 45-80) with histologically confirmed PC (17 localized, 35 metastatic). Germline DNA was isolated from blood lymphocytes or buccal swabs, and targeted next-generation sequencing was conducted with use of a previously validated panel of 30 genes associated with an elevated risk for common cancers (Color Genomics). As a reference for gene aberration frequencies we used the Exome Aggregation Consortium (ExAC) database. Results: The majority of patients (48/52, 92%) had a positive family history of cancer in any relative. Nine deleterious pathogenic mutations were identified in germline DNA samples from 8/52 (15%) patients, affecting the following genes: APC (n = 2, 3.8%), BRCA2 (n = 2, 3.8%), CHEK2 (n = 3, 5.7%), ATM (n = 1, 1.9%), RAD51D (n = 1, 1.9%). APC mutations were significantly more frequent in our cohort compared to the ExAC database (0.3%, p < 0.001). The frequency of DNA repair gene alterations (7/52, 13.5%) was also significantly higher compared to the ExAC database (0.3%, p < 0.001). The median overall survival (OS) between patients with and without germline gene alterations was similar (81.5 versus 74 months, respectively). The presence of heritable gene alterations from the 30-gene panel was significantly more frequent in patients with a positive family history of any cancer (p < 0.001) or prostate, breast, ovarian cancer (p = 0.001) in a first degree relative. Conclusions: The use of a targeted panel of high-susceptibility cancer-associated genes in PC not only confirms the enrichment of germline mutations in men with PC. It can also reveal associations of PC with other cancers which may portend implications for treatment and prognosis.