(UroToday.com) Since 2015, multiple studies together have suggested that approximately a quarter of metastatic castration-resistant prostate cancer (mCRPC) tumors have mutations in DNA damage repair (DDR) genes. These alterations, especially those in genes for homologous recombination repair (HRR), are associated to varying degrees with response to PARP inhibitor therapy. Two PARP inhibitors are now approved for the care of patients with mCRPC and mutations in certain HRR genes: olaparib (based on PROfound trial) and rucaparib (based on TRITON2 trial). Given the significance of alterations in HRR genes in mCRPC, genomic testing for HRR alterations has been included in mCRPC treatment guidelines with the purpose of guiding genetic counseling and therapy selection.

In this poster, Dr. Neal Shore and colleagues describe real-world patterns and predictors of tissue testing for alterations in HRR genes. They focused on the community cancer care setting. Data were collected from the Flatiron Health Electronic Health Record derived database that was collected between 2013 and March 2019, prior to the approval of PARP inhibitor therapy in mCRPC, and focused on testing for alterations in BRCA1, BRCA2, ATM, CDK12, FANCA, and PALB2). The Flatiron database contains information on patient demographics, prostate cancer characteristics, and treatment, as well as genetic testing results.

From the Flatiron database, 5,213 patients with mCRPC were identified, 91% of which were managed at community oncology care centers. Of these patients, 674 (12.9%) underwent testing for the specified HRR gene alterations. Patient characteristics are shown below.

The breakdown of the 674 patients by testing method and number of genes tested is shown below.

BRCA1 and BRCA2 were the most commonly tested genes. A substantial portion of patients underwent only blood/saliva testing (40.5%, capable of detecting germline or circulating tumor DNA) or tumor-tissue testing only (42.1%, capable of detecting germline or tumor tissue DNA alterations). Only 1.8% of patients undergoing blood/saliva testing were tested for all 6 HRR genes, and 69% of tumor-tissue testing covered all 6 genes. Amongst the 286 patients who had negative blood/saliva testing, only 12.6% underwent tumor-tissue profiling, and 5 of these patients (13.9%) had an HRR alteration found.

The most common testing platform utilized was Foundation Medicine, followed by Guardant. Testing rates and the inclusion of more genes increased with time.

The prevalence of HRR alterations found is shown below.

Treatment at an academic medical center or having received multiple prior lines of therapy was associated with a higher likelihood of having HRR mutational profiling. Older age and higher PSA value at diagnosis of mCRPC were significantly associated with a lower likelihood of HRR mutation profiling.

The poster concludes that rates of HRR mutational testing did not increase dramatically with changes to the NCCN guidelines recommending this testing in 2017. Increased awareness of recommendations for testing, especially with the approval of two therapeutic agents contingent upon the presence of HRR alterations, is critical for the care of patients with mCRPC.

Presented by: Neal Shore, MD FACS, Urologist, and Director of the Carolina Urologic Research Center, Myrtle Beach, South Carolina

Written by: Alok Tewari, MD, Ph.D., Medical Oncologist at the Dana-Farber Cancer Institute, at the 2020 European Society for Medical Oncology Virtual Congress (#ESMO20), September 19th-September 21st, 2020

Excerpt from:
ESMO Virtual Congress 2020: Real-World Patterns of Genomic Testing in Patients with Metastatic Castration-R... - UroToday

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