Targeted Proteomics Pipeline Reveals Potential Biomarkers for the Diagnosis of Metastatic Lung Cancer in Pleural Effusion

The ability to discriminate lung cancer malignant pleural effusion (LC-MPE) from benign pleural effusion has profound implications for the therapy and prognosis of lung cancer. Here, we established a pipeline to verify potential biomarkers for this purpose. In the discovery phase, label-free quantification was performed for the proteome profiling of exudative pleural effusion in order to select 34 candidate biomarkers with significantly elevated levels in LC-MPE. In the verification phase, signature peptides for 34 candidates were first confirmed by accurate inclusion mass screening (AIMS). To quantify the candidates in PEs, multiple reaction monitoring mass spectrometry (MRM–MS) with stable isotope-labeled standards (SIS) peptides was performed for the 34 candidate biomarkers using the QconCAT approach for the generation of the SIS peptides. The results of the MRM assay were used to prioritize candidates based on their discriminatory power in 82 exudative PE samples. The five potential biomarkers (ALCAM, CDH1, MUC1, SPINT1, and THBS4; AUC > 0.7) and one three-marker panel (SPINT1/SVEP1/THBS4; AUC = 0.95) were able to effectively differentiate LC-MPE from benign PE. Collectively, these results demonstrate that our pipeline is a feasible platform for verifying potential biomarkers for human diseases.