Since our data reveal that the newly developed anti-CD26 mAbs can specifically stain denatured human CD26 in FFPE tumor cells with reliable clarity and intensity, we then conducted immunohistochemical staining of FFPE CD26-expressing tumor tissues of hepatocellular carcinoma, renal cell carcinoma, prostate adenocarcinoma, colon adenocarcinoma, and lung adenocarcinoma with U16-3 mAb or U38-8 mAb. Here, DPP4 is linked to hereditary clear cell renal cell carcinoma.