Comparative of PD-L1 expression on live single circulating tumor cells with PD-L1 in tumor tissue assessed by immunohistochemistry in advanced NSCLC patients.

e15070 Background: Live single circulating tumor cells (sCTCs) can provide valuable insights matching or differentiated to tissue biology and real-time dynamics of tumors at the clinical level. However, isolating live CTCs in an individual cell with no leucocyte contaminants is extremely challenging. Like tissue-based IHC, sCTCs can provide information on the expression of clinically important markers such as PD-L1 for selecting patients for immune checkpoint inhibitor (ICI) therapy. PD-L1 expression, routinely assessed by IHC, provides a static snapshot of tumor immunology, and is unable to comprehend the dynamics of PD-L1 expression. In contrast, sCTCs may exhibit a real-time dynamic PD-L1 expression for selection of immunotherapy especially when tissue is unavailable. This study compares, PD-L1 expression on tumor tissues when paired with sCTCs captured in non-small cell lung carcinoma (NSCLC) patients. Methods: Retrospectively, we assessed 30 advanced NSCLC patients for the expression of PD-L1 on tissue as well as on sCTC captured and isolated in blood. 20 patients were paired with tissue and blood samples and evaluated for PD-L1 expression, as 10 patients did not yield sufficient tissue. PD-L1 expression on tissue was evaluated using FDA-approved DAKO PD-L1 PharmDx IHC technology. Conversely, true live sCTCs were captured and released using OncoIndx Ikon platform mediated with anti EpCAM antibody and Tf-based platform, an assay in 96 well plates. The PD-L1 expression was measured on fixed sCTCs, and levels of expression of protein were categorized into low, middle, and high based on the intensities. Results: Out of 30 patients, 53 sCTCs were detected in 29 patients, while in 25 patients (83%) sCTCs showed expression of PD-L1. While IHC-based PD-L1 positivity (TPS ≥1) was observed in 15 (75 %) patients. In paired samples, 50 % concordance (45 % positive and 5 % negative) was observed between IHC and sCTC-based PD-L1 detection. Interestingly, 20 % of patients (5/20) were negative for PD-L1 by IHC, demonstrating strong expression of PD-L1 on paired sCTCs. We observed significant intra and inter-patient heterogeneity in PD-L1 expression on sCTCs when the whole sCTC population was considered. PD-L1 expression within the sCTC population varied significantly across low, medium, and high expression levels. High PD-L1 expression was observed in 72%, while medium and low expressions were detected in 15% and 13% of patients, respectively. Conclusions: Analyzing PD-L1 expression on sCTC may provide a feasible alternative to IHC-based PD-L1 detection when tissue biopsy is unavailable or inadequate. Detecting PD-L1 expression on sCTCs may have prognostic applications and importance for patient selection for ICI therapy.