Takana et al. discovered that the frequency of CD26-positive cells, the level of activity staining, and the degree of CD26 messenger ribonucleic acid expression were significantly higher in 57 thyroid samples (pathology: 55 papillary and five follicular carcinomas) than in 58 controls (Graves’ disease) (21). Here, DPP4 is linked to thyroid gland follicular carcinoma.