Liquid biopsy: A community-based oncology practice experience.

Abstract

3527 Background: Liquid biopsy is a promising and minimally invasive genetic test examining plasma circulating tumor DNA. Coupled with the rapidly developing next-generation sequencing (NGS) technologies, it holds the potential for implementation in selecting signal-matched therapeutic options. Methods: A retrospective chart review was conducted on adult patients with advanced solid tumors whose tumors were tested with Guardant360 assay, between December 2018 and December 2019. A total of 178 patients were referred for testing by 12 oncologists within a single community cancer center. Results: Referral rates varied widely (2.25% - 22%). The majority of patients (98%) were tested upfront for molecular marker evaluation, in either newly diagnosed advanced cancer patients, or in recurrent patients without enough tissue for testing. Other patients (2%) were evaluated after failure of 1 st line therapy to assess for acquired mutations. A total of 18 histological types were tested, with lung (LCa; n = 90; 50.56%), breast (BCa; n = 31; 17.42%), and colorectal (CRCa; n = 14; 7.87%) cancers being the most common types. In 86.11% of all tests (n = 180), ≥ 1 alteration was detected, while 13.89 % of tests did not reveal any tumor-related mutation, and were considered negative. The average number of alterations per test was 3.1 (±2.14; n = 481), and varied across types: CRCa (4.36), prostate cancer (2.73), BCa (2.97), and LCa (2.59), had the highest average number of alterations per test. Similarly, LCa (48.44%), BCa (19.13%), and CRCa (12.68%), harbored most of the detected somatic alterations (n = 481). Of all the alterations of practical significance (n = 457), TP53 (32.17%), PIK3CA (8.53%), EGFR (7.66%) and KRAS (7.22%), were the most commonly altered genes. Only 1 patient had a positive MSI-H status, amenable to immune-therapy. Of those with positive test results (n = 155), 31 (20%) had ≥ 1 FDA approved, target-matched therapeutic opportunity. Similarly, 71 patients (45.81%) had ≥ 1 target-matched therapeutic opportunity, outside current indications. Lastly, when no FDA-approved target-matched therapy was available (n = 39), results from liquid biopsy testing offered signal-based clinical trial opportunity in 39/39 patients. Conclusions: Implementation of NGS-based liquid biopsy testing is feasible within a community practice. In the era of precision oncology, such assays have the potential to expedite the efforts towards target-matched therapies and signal-based clinical trial opportunities. Further studies are warranted to identify the most-cost effective testing strategies.