Abstract 3736: Characterization of tumor cells and assessment of PD-L1 expression in pleural effusions of metastatic non-small cell lung cancer patients
Authors: Thompson Jeffrey C. , Savitch Samantha L. , Fan Ryan , Yee Stephanie S. , Powers Christian A. , Yu Gordon , Gebrian Lauren , Rao Chandra , Gross Steve , Feldman Michael , Vachani Anil , Carpenter Erica L. 
Published: July 2017

Abstract
Introduction: Malignant pleural effusions (MPE) occur as a frequent complication of advanced non-small cell lung cancer (NSCLC), and denote a poor prognosis. Cytological evaluation of MPEs has a sensitivity of only 40-60%. The CellSearch technology (Janssen Diagnostics, LLC) is an FDA approved method of detecting rare circulating tumor cells (CTCs) in blood. Assessment of pleural fluid samples using CellSearch provides an approach to enrich often undetectable CTCs and phenotype these cells for markers of interest. PD-L1 staining of tumor tissue is essential for determining patient candidacy for checkpoint inhibitor therapy, however, tissue can often be difficult to obtain. Here, we demonstrate the feasibility of applying the CellSearch CTC enrichment platform to measure PD-L1 expression and enumerate tumor cells in MPE of NSCLC patients.
Methods: This was a single center, prospective observational study of NSCLC patients with a pleural effusion. The anti-human CD274 (PD-L1) antibody (Biolegend) was used as a marker with the CellSearch CXC CTC kit and was detected in the open 4th channel of the CellTracks Analyzer. Determination of CTC PD-L1 expression was validated through peripheral blood spiking experiments. 7.5ml of pleural fluid was collected from NSCLC patients, preserved in CellSave tubes and processed within 72 hours. Identification and enumeration of CTCs was performed using the CellTracks Analyzer. We then compared CellSearch results to conventional cytological analysis.
Results: Pleural effusion samples from 66 patients between the ages of 43 and 80 (median=69) were obtained following thoracentesis. The majority of patients were former (40; 60.6%) or never (21; 31.8%) smokers. At the time of effusion, 23 (34.8%) patients were on a therapeutic regimen: 10 (15.2%) were receiving chemotherapy, 9 (13.6%) were on an EGFR or ALK TKI, and 5 (7.6%) were on a checkpoint inhibitor. CTCs were detected in 63 of 66 samples using the CellSearch system. Among the 66 pleural effusions, cytological evaluation determined 40 samples were malignant and 26 were benign. CellSearch detected more CTCs in patients with a MPE (median 1798, range: 7 to 114,920) compared to patients with a benign effusion (median 8, range: 0 to 953; p=0.005). In the MPE group, 18 (45.0%) samples demonstrated &gt;10% PD-L1 positivity with 9 (22.5%) samples showing &gt;50% PD-L1 positivity.
Conclusion: The CellSearch CTC enumeration and characterization platform can be successfully adapted for detection of CTCs in MPE of NSCLC patients. Our preliminary results suggest this approach may be a useful, non-invasive diagnostic adjunct for the determination of a MPE and assessment of PD-L1 expression in NSCLC patients. Further study is warranted to determine what role this test could play in assessing patients for checkpoint inhibitor therapy and its relationship with tissue based tests.
Citation Format: Jeffrey C. Thompson, Samantha L. Savitch, Ryan Fan, Stephanie S. Yee, Christian A. Powers, Gordon Yu, Lauren Gebrian, Chandra Rao, Steve Gross, Michael Feldman, Anil Vachani, Erica L. Carpenter. Characterization of tumor cells and assessment of PD-L1 expression in pleural effusions of metastatic non-small cell lung cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3736. doi:10.1158/1538-7445.AM2017-3736