Tumor testing in men with prostate cancer to predict for germline DNA-damage repair mutations

229 Background: Current guidelines recommend genetic testing for patients (pts) who have BRCA1/2 mutations on tumor-only testing, where germline is not subtracted. The clinical utility of this approach, and possible inclusion of other DDR genes associated with cancer susceptibility, has not been examined in men with prostate cancer. Methods: Pts with mostly advanced prostate cancer were prospectively enrolled to a matched tumor-germline DNA sequencing protocol and consented for disclosure of germline results. Germline analysis was done with an institutional, CLIA-certified next generation sequencing (NGS) platform (MSK-IMPACT) and analyzed for likely pathogenic or pathogenic germline mutations in at least 76 cancer susceptibility genes. Clinical data was retrieved from the medical record. We report on the frequencies in the germline and in the tumor of a subset of DDR genes. Results: 1243 men had analysis of both germline and tumor. Median age 64 (range 35-90). 12% had a second malignancy and 40% reported a relative with prostate cancer. 19% were of Ashkenazi Jewish (AJ) descent. 330 (27%) had any mutation in BRCA1/2, ATM, CHEK2, PALB2, RAD51C, RAD51D, MSH2, MSH6, MLH1, PMS2. 127 (10%) had a germline mutation, of which 36% were AJ founder mutations. For each gene, the percentage of mutations found in germline and tumor is shown in the table. Conclusions: Of prostate cancer pts found to have any DDR mutation on tumor-germline testing, 29% had a germline mutation. Proportion of germline mutations was highest for PALB2, CHEK2 and BRCA2. These findings not only support germline testing when BRCA1/2 mutations are found tumor-only sequencing, but also support germline testing when other DDR mutations are seen. Clinical trial information: NCT01775072. [Table: see text]