Diagnostic yield of germline genetic testing following tumor testing in prostate cancer patients.

Abstract

1591 Background: NCCN guidelines recommend germline testing for patients with localized or advanced prostate cancer meeting family history or clinical/pathologic criteria. However, the guidelines for somatic molecular analysis generally consider advanced disease only, primarily to inform therapy. As the analytical and clinical specifications of both testing modalities differ accordingly, we examined the results of germline testing following prior somatic testing. Methods: We reviewed somatic and germline variants in an otherwise unselected consecutive series of patients who: (a) had a current or previous diagnosis of prostate cancer; (b) had undergone tumor sequencing; and (c) were referred for germline testing. Indications for germline testing included: potential germline origin of somatic test result, treatment or surgical planning, personal or family history, and patient concern. Results: 208 patients met study criteria of whom 81 (39%) harbored a pathogenic germline variant (PGV) in a cancer predisposition gene. Certain genes were more likely to harbor germline variants, and 98% (81) of PGVs were potentially actionable (Table). 9.6% of PGVs were not reported by somatic testing, reflecting analytical limitations of the somatic testing. Of note, 11 patients (14%) had PGVs identified after diagnosis of a subsequent primary malignancy. Conclusions: The high PGV rate of 39% was unexpected, given reported rates of 11.8% in patients with metastatic prostate cancer and 6% in high-risk localized disease (NCCN)--even considering potential clinician ascertainment bias. This finding, the potential clinical utility of 98% of PGVs identified, the significant proportion unreported by somatic testing, and the fraction of patients diagnosed with a PGV after a subsequent malignancy all suggest that germline testing is an underutilized tool in the care of prostate cancer patients and their families. [Table: see text]