FAP and cancer: The differential Gly-Pro-p-nitroanilide hydrolysis in both adherent cells and the supernatant, which formed p-nitroaniline in vitro, suggests the existence of DPPIV/CD26 activity in SiHa (HPV 16-positive), HeLa (HPV 18-positive), C33A (HPV-negative) cancer cells and HaCaT (non-tumorigenic control cells).