Frequencies of actionable alterations found by somatic tumor sequencing in veterans with metastatic prostate cancer.

Abstract

178 Background: Prostate cancer comprises one third of male Veteran cancers and is their second leading cause of cancer death. Metastatic prostate cancer is lethal. Next Generation Sequencing (NGS) of somatic tumors is recommended for metastatic prostate to identify actionable alterations targeted with approved therapies. Veterans with prostate cancers harboring alterations in genes involved in the DNA damage response (e.g. BRCA1/2) or high microsatellite instability (MSI-High) may be eligible for PARP inhibitors or checkpoint blockade immunotherapy, respectively. Potential candidates may be identified for ongoing clinical trials of novel precision oncology approaches. Methods: This is a retrospective analysis of clinical, genomic, demographic data from Veterans with metastatic prostate cancer who underwent somatic NGS using the Foundation Medicine NGS platform from 2019-February 2021. To be included, prostate cancer was submitted diagnosis for the NGS testing and metastatic disease determined by the VINCI natural language processing tool. Variables included demographic, clinical, and pathological characteristics (self-identified race/ethnicity, age, rurality of residence, Gleason score, specimen site, other cancer diagnosis, mutation frequency). Primary outcome was mutation rates in homologous recombination (HR) genes under current FDA approval for olaparib (ATM, BARD1, BRCA1, BRCA2, BRIP1, CDK12, CHEK1, CHEK2, FANCL, PALB2, RAD51B, RAD51C, RAD51D, RAD54L) or MSI-High. Raw variant data, submitted diagnosis, and clinical data were extracted from the NGS reports and harmonized for further variant annotation. Variant data included chromosome, position, reference and alternate allele, total depth, variant allele depth, and quality scores. Variants were annotated using ANNOVAR. Likely oncogenic and oncogenic mutations were identified using OncoKB. Results: 1,597 Veterans with metastatic prostate cancer underwent FMI NGS testing (63% White, 33% African American, 4% other). Median age was 66 years, 78.6% of cases from >60 years. Of the 1,597 who underwent blood or tumor testing, at least one likely oncogenic mutation in an HR gene under FDA approval for olaparib was found in 369 (23.1%) of Veterans (19% of tissue-based tests, 32.9% of blood-based tests). Of 651 liquid biopsy tests with at least one HR gene mutation, 125 of 214 (52%) had mutations at a variant allele frequency (VAF) <0.5% or were found in an MSI-High sample that could indicate a spurious mutation due to clonal hematopoiesis. 33 patients (2.1%) were MSI-High, (21 tissue-based and 12 blood-based). Frequencies of alterations in ATM (3.6%), CDK12 (5.6%), and BRCA2 (4%) in tissue-based tests were not significantly different from those reported in other series. Conclusions: NGS of somatic tumors from Veterans with metastatic prostate cancer identifies alterations that impact management and clinical outcomes.