Cellular Expression of PD-L1 in the Peripheral Blood of Lung Cancer Patients is Associated with Worse Survival

Background: Lung cancer treatment has become increasingly dependent upon invasive biopsies to profile tumors for personalized therapy. Recently, tumor expression of programmed death-ligand 1 (PD-L1) has gained interest as a potential predictor of response to immunotherapy. Circulating biomarkers present an opportunity for tumor profiling without the risks of invasive procedures. We characterized PD-L1 expression within populations of nucleated cells in the peripheral blood of lung cancer patients in hopes of expanding the role of liquid biopsy in this setting. Methods: Peripheral blood samples from a multi-institutional prospective study of patients with clinical diagnosis of lung cancer were subjected to cytomorphometric and immunohistochemical evaluation using single-cell, automated slide-based, digital pathology. PD-L1 expression was determined by immunofluorescence. Results: PD-L1 expression was detected within peripheral circulating cells associated with malignancy (CCAM) in 26 of 112 (23%) non–small cell lung cancer patients. Two distinct populations of nucleated, nonhematolymphoid, PD-L1–expressing cells were identified; cytokeratin positive (CK+, PD-L1+, CD45−) and cytokeratin negative (CK−, PD-L1+, CD45−) cells, both with cytomorphometric features (size, nuclear-to-cytoplasm ratio) consistent with tumor cells. Patients with >1.1 PD-L1(+) cell/mL (n = 14/112) experienced worse overall survival than patients with ≤1.1 PD-L1(+) cell/mL (2-year OS: 31.2% vs. 78.8%, P = 0.00159). In a Cox model adjusting for stage, high PD-L1(+) cell burden remained a significant predictor of mortality (HR = 3.85; 95% confidence interval, 1.64–9.09; P = 0.002). Conclusions: PD-L1 expression is detectable in two distinct cell populations in the peripheral blood of lung cancer patients and is associated with worse survival. Impact: These findings could represent a step forward in the development of minimally invasive liquid biopsies for the profiling of tumors. Cancer Epidemiol Biomarkers Prev; 26(7); 1139–45. ©2017 AACR.