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Spindle Epithelial Tumour with Thymus-like Differentiation (Settle): A Distinctive Malignant Thyroid Neoplasm: A Case Report

Nikhil Kantilal Majethia*

The spindle epithelial tumor with thymus-like element (SETTLE) is a very rare neoplasm related to the thyroid of young individuals. In 1991, Chan and Rosai unified the concept of SETTLE when they described 8 neoplasms situated in the neck and thyroid of children and young adults, previously diagnosed as malignant teratoma of the thyroid, thyroid spindle cell tumor with mucous cysts or thyroid thymoma. SETTLE is a distinct low-grade neoplasm, believed to be derived from branchial pouch or thymic remnants, with only 1 case report showing association with epithelium-lined cysts of possible branchial pouch derivation. It belongs to a group of cervical lesions that includes ectopic cervical thymoma, ectopic hamartomatous thymoma and carcinoma with thymus-like element (CASTLE). This tumor is composed predominantly of spindle and epithelioid cells with glandular or ductular structures lined by a mucinous or respiratory epithelium. In spite of indolent growth, SETTLE may give metastases many years after the diagnosis. Therefore, a long-term follow-up is required. We present one case, the first report from Sion Hospital, of a patient who has benign clinical course and tumoral features suggestive of a myoepithelial differentiation. The clinicopathologic features of the case reports in the literature are also reviewed. This case report showed the first report from our hospital and the possibility of a myofibroblastic differentiation. The SETTLE is among four tumors related to the thyroid, easily differentiated by clinicpathologic correlation. It is a lowgrade malignant neoplasm, with epithelial differentiation confirmed by immunohistochemical. Despite all the descriptions in the literature, this tumor remains with uncertain histogenesis and lacking convincing proof of thymic differentiation or branchial pouch derivation. SETTLE can metastasize a long time after the surgical resection. Because of this, the patients need long-term follow-up, with particular attention to monitoring the lungs.