Prevalence of Germline Variants in Prostate Cancer and Implications for Current Genetic Testing Guidelines.

Importance: Prostate cancer is the third leading cause of cancer-related death in men in the United States. Although serious, most of these diagnoses are not terminal. Inherited risk for prostate cancer is associated with aggressive disease and poorer outcomes, indicating a critical need for increased genetic screening to identify disease-causing variants that can pinpoint individuals at increased risk for metastatic castration-resistant prostate cancer.

Objective: To identify positive (pathogenic, likely pathogenic, and increased risk) germline variants in a large prostate cancer cohort and to evaluate the usefulness of current practice guidelines in recognizing individuals at increased risk for prostate cancer who would benefit from diagnostic genetic testing.

Design, Setting, and Participants: Cross-sectional study of data from 3607 men with a personal history of prostate cancer who underwent germline genetic testing between 2013 and 2018 and were unselected for family history, stage of disease, or age at diagnosis. Referral-based testing was performed at a Clinical Laboratory Improvement Amendments/College of American Pathologists-certified diagnostic laboratory. All analysis took place between February 2017 and August 2018.

Main Outcomes and Measures: The frequency and distribution of positive germline variants, and the percentage of individuals with prostate cancer who met National Comprehensive Cancer Network (NCCN) guidelines for germline genetic testing.

Results: Of 3607 men (mean [SD] age at testing, 67 [9.51] years; mean age at diagnosis, 60 [9.05] years) with a personal diagnosis of prostate cancer who were referred for genetic testing, 620 (17.2%) had positive germline variants, of which only 30.7% were variants in BRCA1/2. Positive variants in HOXB13, a gene associated only with prostate cancer risk, were identified in 30 patients (4.5%). DNA mismatch repair variants with substantial known therapeutic implications were detected in 1.74% of variants in the total population tested. Examination of self-reported family histories indicated that 229 individuals (37%) with positive variants in this cohort would not have been approved for genetic testing using the NCCN genetic/familial breast and ovarian guidelines for patients with prostate cancer.

Conclusions and Relevance: Current NCCN guidelines and Gleason scores cannot reliably stratify patients with prostate cancer for the presence or absence of pathogenic germline variants. Most positive genetic test results identified in this study have important management implications for patients and their families, which underscores the need to revisit current guidelines.