NONINVASIVE ENCAPSULATED ANAPLASTIC THYROID CARCINOMA PROMISING AN EXCELLENT CLINICAL COURSE: A CASE REPORT AND REVIEW OF THE LITERATURE

Noninvasive encapsulated anaplastic thyroid carcinomas (NE-ATCs) have been described in few case reports, and consistently associated with favorable outcome compared to the classical ATCs. Our aim is to remark a rare histological finding in ATCs, encapsulation, which has been associated with a favorable outcome. We have documented a rare case of an NE-ATC with its clinical, pathological, and molecular features. We also provided a thorough discussion of all the encapsulated ATCs reported in the literature. A 50-year-old woman with an unremarkable medical history, who presented with a thyroid nodule, and diagnosed as "follicular lesion of undetermined significance" by fine needle aspiration biopsy. The patient was lost to follow-up for six years and revisited upon her neck disturbances and underwent total thyroidectomy. Sections of the right lobe revealed a grossly encapsulated nodular lesion, measuring 75x55x55 mm. Histologically, the tumor consisted of both carcinomatous and sarcomatous components supported by immunohistochemical stains. Necrosis and atypical mitotic figures were evident. Capsular and/or vascular invasion was not identified. There were no BRAF codon 600, KRAS, NRAS mutations and RET/PTC rearrangement. During three-month follow-up, the patient was free of disease without adjuvant therapy. Encapsulated ATCs tend to follow a favorable clinical course and may deserve conservative treatment approaches.