In sitagliptin-treated CD26-/- mice, the anti-tumor effect of the Th17 cells was diminished and 9/10 mice lost control of their tumor by day 78 post-treatment (survival of CD26-/- vs. CD26-/- +sitagliptin p=0.005, Mantel-Cox Logrank test). This evidence concerns the gene DPP4 and neoplasm.