MDM2 and thyroid tumor: The aim of this study has been to verify whether p90RSK is capable of phosphorylating MDM2 in serine 166 and to investigate the role of p90RSK in regulating the p53 pathway, especially in thyroid tumors in which the MAPK pathway is constitutively active and in which the development of specific drugs aimed at inhibiting the kinase activity of p90RSK could represent a new way of inhibiting tumorigenesis.