Sensitivity of PD-L1 analysis from pleural effusion in non-small cell lung cancer

Background: The detection of PD-L1 in non-small cell lung cancer (NSCLC) is of great relevance for individualized therapy and has so far been performed using immunohistochemical analysis (IHC). With accompanying pleural effusion, the immunocytochemical analysis (ICC) could be of additive diagnostic value. Methods: 50 patients (17 women, 70±10 years, 26±5 kg/m²) with highly suspected NSCLC and pleural effusion were examined. PD-L1 expression of IHC and ICC samples were compared using the PD-L1 IHC 22C3 pharmDx Kit (Dako). Sensitivity and specificity of tumour and PD-L1 detection of ICC was determined with IHC as reference. PD-L1 was quantified according to percent of tumour cells expressing PD-L1. Due to different approval statuses of available immune checkpoint inhibitors, we considered different cut-offs for PD-L1 positivity. Results: Regarding the detection of malignancy, 7 cases with inconclusive ICC results were defined as tumour negative. Failed PD-L1 analyses were defined as PD-L1-negative. Conclusion: The detection of tumour cells in pleural punctate shows good sensitivity. PD-L1 detection is less sensitive but may still contribute to the identification of PD-L1-positive lung carcinoma. In case when invasive diagnostics (bronchoscopy, thoracoscopy) are not feasible, ICC of pleural punctate may offer a clinically valuable alternative to detect PD-L1-positive lung carcinoma with the option for 1st-line immune checkpoint inhibitor monotherapy.