Poorly differentiated thyroid cancer (PDTC) and anaplastic thyroid cancer (ATC) are rare but highly aggressive malignancies with an extremely short survival. Poor prognosis is due to their unlimited growth, invasion, migration and resistance to common anticancer therapies. Advances in understanding the molecular alterations in thyroid carcinomas led to development of new therapeutic strategies such as kinase inhibitors. Although several of these compounds have been approved by FDA and EMA for the treatment of radioactive-iodine refractory differentiated thyroid cancer (DTC) and medullary thyroid cancer (MTC), no significant clinical efficacy with targeted therapies have been observed in those patients.Herein, we review and summarize the preclinical in vitro evidences of mechanisms of resistance to kinase inhibitors currently used in PDTC and ATC patients.