"Insular" carcinoma of thyroid. A subset of anaplastic thyroid malignancy with a less aggressive clinical course.

Insular carcinoma of the thyroid appears to represent an entity situated morphologically and biologically in an intermediate position between the well-differentiated and undifferentiated (anaplastic) tumors. The retention of I-131 concentrating ability by this variant, unlike anaplastic, is very encouraging and amenable to detection and therapy by radioiodine after initial aggressive surgery. A 46-year-old man with a histologic label of anaplastic thyroid carcinoma has had an unusually prolonged disease-free survival and histopathologic review confirmed insular carcinoma. Postoperative radioiodine evaluation revealed avid concentration of tracer in the thyroid bed. Thus, it is possible to ablate with radioiodine. The insular carcinoma should be considered as a distinct clinicopathologic entity and widespread awareness of this variant of tumor may help pathologists, surgeons, and nuclear medicine practitioners to aggressively treat the condition after initial diagnosis.