Summary
Thyroid cancer is the most common endocrine malignancy and its incidence goes on increasing worldwide. The majority of thyroid tumours
comprise well-differentiated (papillary and follicular) thyroid carcinomas that usually carry an excellent prognosis, while a minority progress to
poorly differentiated carcinoma (PDTC) and, ultimately, to the highly aggressive and lethal undifferentiated carcinoma (UTC). Recently, some
major advances have been made on the histologic and imunohistochemical identification, as well as on the molecular characterization of PDTC
and UTC. In this review we summarize the most recent immunohistochemical and molecular findings in PDTC and UTC, giving a particular
emphasis to the diagnostic and prognostic meaning of the genetic alterations.