Mesothelin—a 40 kDA cell surface glycoprotein expressed by mesothelial cells—another putative pleural effusion biomarker for mesothelioma—displayed a similar diagnostic effectiveness in our study with an AUC of 0.49 (95% CI: 0.38–0.64), which was lower than the previously reported AUCs ranging from 0.70 to 0.93 [32]. The gene discussed is MSLN; the disease is mesothelioma.