The present invention relates to diagnostic, therapeutic and prognostic methods for thyroid cancers. In one embodiment, the present invention provides a method for treating a an anaplastic thyroid cancer (ATC) patient comprising the step of administering to the patient an effective amount of an anaplastic lymphoma kinase (ALK) inhibitor. In another embodiment, a method for diagnosing ATC in patient comprises the step of performing an assay on a biological sample from the patient to identify the presence or absence of a C3592T and/or a G3602A mutation in exon 23 of the ALK gene according to SEQ ID NO:6, wherein the presence of either of both of the mutations correlates with a diagnosis of ATC in the patient.
