It is known that the CD26 molecule and serum dipeptidyl peptidase IV (DPP IV) activity are inversely correlated with disease activity in patients with systemic lupus erythematosus and may play a role in the pathophysiology of hepatocellular carcinoma, colorectal cancer, prostate cancer, and malignant mesothelioma [99,100,101,102]. Here, DPP4 is linked to malignant mesothelioma.