Thyroid spindle epithelial tumor with thymus‐like differentiation (SETTLE): Is cytopathological diagnosis possible?

Abstract

Spindle epithelial tumor with thymus-like differentiation (SETTLE) is a rare tumor of the thyroid gland which occurs predominantly in children, adolescents, and young adults. It usually presents as a painless neck or thyroid mass and only exceptionally as a diffusely enlarged thyroid gland, without metastatic disease at diagnosis. We report on the case of 12-yr-old girl who had diffusely enlarged thyroid gland for about 1 yr and was initially treated for thyroiditis. Fine-needle aspiration biopsy (FNAB) was performed 8 mo after the first admission. Cytological examination of smears showed unusual morphological features. FNAB smears were cellular, with dissociated cells, naked oval nuclei, aggregates, and groups. Three main cell types were observed: spindle, epithelioid, and epithelial. These cells were uniform, cytologically bland, with few mitotic figures. The distinction between these cells was not always unequivocal. In the background of the smears abundant red extracellular material in the form of fine, dust-like granules and irregular patches were present. It was also observed in some aggregates and groups of tumor cells. Spindle and epithelioid cells were immunocytochemically diffusely pan-cytokeratin-positive. In the differential diagnosis, medullary thyroid carcinoma and SETTLE were suggested. The final histological diagnosis was SETTLE. In cases of SETTLE presented as a diffuse thyromegaly the correct diagnosis may be delayed because clinically and ultrasonographically thyroiditis is suspected. To avoid such a delay, FNAB should be used preoperatively. It can provide specific cytological diagnosis based on morphological features and certain immunocytochemical characteristics of the tumor.

Solitary fibrous tumor of the thyroid: Cytopathologic findings and differential diagnosis

“…There a handful of reports on leiomyoma and schwannoma of the thyroid. 14,15 Other entities in the differential diagnosis of SFT include medullary carcinoma, hemangiopericytoma, 16 ectopic thymoma, spindle epithelial tumor with thymus-like differentiation (SETTLE), 17 and hyalinizing trabecular adenoma of the thyroid. 18 There have been a limited number of reports on the cytopathologic features of pleural and extrapleural SFTs.…”

Spindle epithelial tumor with thymus-like elements of the thyroid: a multi-institutional case series and review of the literature

“…In addition to morphology, immunohistochemistry is important for making the diagnosis of SETTLE. The tumor is typically positive for cytokeratin, vimentin, smooth muscle actin, and muscle-specific actin [2,3,[14][15][16][17][18]. Spindle epithelial tumor with thymus-like elements is typically negative for other markers of thyroid malignancy including thyroglobulin, thyroid transcription factor-1, calcitonin, carcinoembryonic antigen, and S-100.…”

Thyroid spindle epithelial tumor with thymus-like differentiation (SETTLE): case report and review

“…In spite of the disease progression with metastasis development, low mortality rates are observed, demonstrating the indolent course of the tumor. SETTLE may not produce metastasis until many years after the diagnosis (mean of 11 years) and according to case reports with follow-up information, the overall rate of metastasis is of about 20% (2,(8)(9)(10)(12)(13)(14)(15). Otherwise, when the analysis is made only on patients with more than 5 years of follow-up, the incidence increases to 50% (8,(12)(13)(14) with 2 patients developing metastasis more than 20 years after the diagnosis (13,14).…”

“…Metastatic spread is reported to lung, mediastinum, local lymph nodes and kidney. The principal site of metastasis is the lung, which represents more than 60% of the metastasis sites (2,8,10,12,14). The gap between diagnosis and detection of metastasis varies from a few months after the primary tumor manifestation to 25 years (14,15).…”