Circulating tumour cells and PD-L1-positive small extracellular vesicles: the liquid biopsy combination for prognostic information in patients with metastatic non-small cell lung cancer

Background Circulating tumour cells (CTCs), circulating tumour DNA (ctDNA), and extracellular vesicles (EVs) are minimally invasive liquid biopsy biomarkers. This study investigated whether they predict prognosis, alone or in combination, in heterogenous unbiased non-small cell lung cancer (NSCLC) patients. Methods Plasma samples of 54 advanced NSCLC patients from a prospective clinical trial. CtDNA mutations were identified using the UltraSEEK™ Lung Panel (MassARRAY® technology). PD-L1 expression was assessed in small EVs (sEVs) using an enzyme-linked immunosorbent assay. Results At least one ctDNA mutation was detected in 37% of patients. Mutations were not correlated with overall survival (OS) (HR = 1.1, 95% CI = 0.55; 1.83, P = 0.980) and progression-free survival (PFS) (HR = 1.00, 95% CI = 0.57–1.76, P = 0.991). High PD-L1 + sEV concentration was correlated with OS (HR = 1.14, 95% CI = 1.03–1.26, P = 0.016), but not with PFS (HR = 1.08, 95% CI = 0.99–1.18, P = 0.095). The interaction analysis suggested that PD-L1 + sEV correlation with PFS changed in function of CTC presence/absence ( P interaction = 0.036). The combination analysis highlighted worse prognosis for patients with CTCs and high PD-L1 + sEV concentration (HR = 7.65, 95% CI = 3.11–18.83, P < 0.001). The mutational statuses of ctDNA and tumour tissue were significantly correlated ( P = 0.0001). Conclusion CTCs and high PD-L1 + sEV concentration correlated with PFS and OS, but not ctDNA mutations. Their combined analysis may help to identify patients with worse OS. Trial registration NCT02866149, Registered 01 June 2015, https://clinicaltrials.gov/ct2/show/study/NCT02866149 .