DPP4 and lung adenocarcinoma: DPP4 is upregulated in many aggressive types of T-cell malignancies (9), esophageal adenocarcinoma (10), lung adenocarcinoma (11), thyroid carcinoma (12), and prostate cancer (13), and a high level of DPP4 is indicative of poor prognosis for papillary thyroid carcinoma (14), urothelial carcinoma (15), and colorectal cancer (16).