DPP4 and neoplasm: NPY released from peritumoral hepatocytes favored, through Y5R, tumor progression; tumor growth factor (TGF)-β1 increased NPY expression in hepatocytes and promoted Y5R expression in invasive tumor cells, and the cleavage of NPY by dipeptidyl peptidase IV, upregulated in hepatocellular carcinoma, increased Y5R activation and function [160].