NPY and neoplasm: Ewing sarcoma intratumoral blood vessels expressed Y1R [139]; Ewing sarcoma cells express NPY, Y1R, and Y5R, and the peptide via both receptors promoted the death of tumor cells, which was mediated by poly(ADP-ribose polymerase) (PARP-1) and apoptosis-inducing factor (AIF) [10,138,139,140].