['S100A8 plays a role in various functions of myeloid cells by forming a heterocomplex with S100A9. S100A8 and S100A9 are also known to be overexpressed in certain species of carcinomas.', 'In this study, the protein expression of S100A8 as well as that of S100A9 was investigated in thyroid tumors.', 'All of the undifferentiated carcinomas were immunopositive for S100A8 and S100A9 and overlap between staining patterns of both proteins was observed. In poorly differentiated carcinomas, all the cases were negative for S100A8, while slight immunopositivity of S100A9 was seen in 2 cases. Papillary carcinoma, follicular carcinoma, follicular adenoma and medullary carcinoma and normal follicules were negative for both proteins.'] Is s100A8 and S100A9 expression a crucial factor for dedifferentiation in thyroid carcinoma?