Abstract 3383: Liquid biopsy for PDL-1 status by analysis of cfRNA: Clinical data from a large community practice

Abstract

Abstract PD-L1 testing via immunochemistry has become a widely used tool to predict response to immune checkpoint inhibitor (ICI) therapy in many tumor types. However this marker can be expressed heterogeneously, and can vary with time, treatment effects, and local factors including cytokine expression. Gene expression profiles of immunologically active genes are currently being studied to more accurately predict response to ICI treatment. To evaluate a potentially more straightforward way to accomplish this, we utilized an assay of cfRNA in plasma for PD-L1, utilizing a real-time PCR based assay (Circulogene, Inc, Birmingham, AL). The demonstrated limit of detection for PD-L1 RNA was 1 copy/ul. Results were reported as either not detected, or low at over 1%, or high at over 50%. We used the PCR 30th percentile Ct value corresponding to a tissue IHC PD-L1 of>50%, and the 66th percentile Ct value corresponding to a tissue PD-L1 expression of >1%. We then collected data on over 400 patients over a two year period at a large community oncology practice and at a university clinic (Florida Cancer Specialists and Atrium Health/Wake Forest-Baptist Comprehensive Cancer Center) who had a clinical necessity for molecular testing in a commercially available setting with a CLIA certified lab. In some cases the corresponding tissue PD-L1 testing was also available, and may have been either positive or negative.To date 41 patients have been found to have high levels of cfRNA for PD-L1. Their clinical course has been analyzed using the electronic medical record. Some patients have received standard of care therapy, and some have been given CPI therapy with or without chemotherapy, if the attending oncologist felt this to be the best palliative option. These include tumors such as CRPC, metastatic low grade neuroendocrine carcinoma and HR+ metastatic breast carcinoma, that have rarely been treated successfully with CPI therapy. Tumor types - all are stage IV solid tumor patients: 19 NSCLC, 7 breast carcinoma, 3 colorectal cancer, 3 castrate resistant prostate carcinoma, 9 other tumor types.Data collection for tumor response or clinical benefit on the 41 patients is ongoing and will be presented at the meeting, and compared to published CPI response data using standard tissue IHC testing. Citation Format: Lowell L. Hart, Magali Van den Bergh. Liquid biopsy for PDL-1 status by analysis of cfRNA: Clinical data from a large community practice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3383.