ABSTRACT
Malignant cancers of thyroid develop from either follicular or parafollicular cells. Follicular cell–originated cancers can be well differentiated (papillary or follicular), which have functions like iodine uptake, thyroglobulin synthesis and thyroid-stimulating hormone dependence, and by acquiring various genetic and somatic mutations become undifferentiated where all the three functions of follicular cells are lost. Poorly differentiated thyroid carcinoma (PDTC) is an intermediated entity that is classified in between well and undifferentiated in terms of morphologic appearance and biological behavior. PDTC are rare tumors that can have a rapid and fatal outcome. Most of the confusion and controversy surrounding the PDTC has cleared after World Health Organization (WHO) accepted it as a separate entity in 2004, and later with Turin criteria defining the definition. The TNM staging of thyroid cancer has both differentiated and undifferentiated (anaplastic) cancers, but it is lacking the PDTC. These patients have RAS, BRAF, P53 and TERT mutations. A complete surgery with resection of all gross disease and compartment-oriented lymph node dissection with adjuvant radioiodine therapy in radioiodine avid lesions are the key components of initial therapy. Adjuvant EBRT can be considered in patients with gross residual locoregional disease or at a high risk of recurrence.
