Insular carcinoma of the thyroid. An uncommon but aggressive neoplasm

Insular carcinoma of the thyroid is an infrequent entity, named in 1984 by Carcangiu when he described its characteristic histology. Clinically and morphologically it is considered to be in an intermediate position between well-differentiated carcinoma of the thyroid (papillary or follicular) and undifferentiated or anaplastic carcinoma of the thyroid. However, most authors believe it to be an independent entity. The prognosis of this tumor is worse than that of classic carcinoma of the thyroid, and most authors advise aggressive therapy, which in some cases can achieved prolonged survival. We describe 2 patients who experienced recurrence after treatment for the primary tumor. The recurrences were treated but the clinical courses differed.