PD-L1 profiling of circulating tumor cells for immune checkpoint inhibitor therapy in gastroesophageal cancers.

Abstract

29 Background: Selection of Immune Checkpoint Inhibitor (ICI) therapies in Gastroesophageal cancers are based on IHC based detection of PD-L1 expression in tumor tissue. Invasive biopsy to obtain tumor tissue for IHC is associated with procedural risks, sequelae and expenses. Prior efforts at PD-L1 profiling of Circulating Tumor Cells (CTCs) have been constrained by low CTC yields. We employed a novel approach for harvesting sufficient CTCs from Gastroesophageal cancers that permit PD-L1 profiling by Immunocytochemistry (ICC). Methods: 15 ml peripheral blood was collected from 106 patients among whom 20 were diagnosed with gastric adenocarcinomas (AD) and 86 with either esophageal AD or esophageal squamous cell carcinomas (SCC). CTCs were enriched from PBMCs via an epigenetically acting stabilization process which induced apoptosis in non-malignant cells and conferred survival privilege on apoptosis-resistant CTCs, which were harvested and confirmed by immunostaining for EpCAM and pan-CK positivity. Deep ICC profiling of CTCs was performed with organ-specific markers as well as PD-L1:22c3 and PD-L1:28-8 clones. Results: Viable CTCs could be enriched and harvested in 103 out of 106 samples (97.2%) regardless of metastatic or treatment status. Deep ICC and PD-L1 profiling could be performed in all 103 samples (100%). PD-L1 expression was quantitatively assigned as ‘Low’, ‘Moderate’ or ‘High’. Among the 19 gastric ADs, 5 (26.3%) samples were positive for PD-L1:22c3 and 2 (10.5%) were positive for PD-L1:28-8; all gastric ADs were ‘Low’ for either PD-L1 subtype. Among the 84 esophageal carcinomas (AD+SCC), 32 samples (38.1%) were positive for PD-L1:22c3 (26 Low + 5 Moderate + 1 High) and 16 (19.1%) were positive for PD-L1:28-8 (11 Low + 5 Moderate). Conclusions: CTCs in Gastroesophageal cancers can be considered for evaluating PD-L1 expression in patients where ICI therapies are otherwise viable.