Because soluble mesothelin‐related protein (SMRP) is currently the best diagnostic biomarker for mesothelioma [20], we also measured SMRP concentration in PEs by ELISA and found a significant but weak correlation between IL‐7 and SMRP levels in MPM (Spearman r = 0.279; P = 0.0176) (Fig. S10A). Here, MSLN is linked to mesothelioma.