Early Metastasizing Spindle Epithelial Tumor with Thymus-like Differentiation (SETTLE) of the Thyroid

Abstract

Spindle epithelial tumor with thymus-like elements is a rare thyroid lesion of children and young adults thought to be derived from branchial pouch remnants or foci of ectopic thymus. The lesion is poorly understood, and although it was originally believed to follow an indolent clinical course, its potential for late metastasis is becoming generally acknowledged. We have recently seen a unique case of this rare tumor in an 11-year-old boy, in which an unexpected and salient feature is the presence of a micrometastasis in a single lymph node at presentation. With the exception of 1 case with extensively infiltrative tumor and metastatic disease at the time of onset, in all other cases dissemination occurred years after surgical resection of the primary lesion. We review all previously reported cases and provide a detailed study of the histologic and ultrastructural appearances of this lesion.

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

“…Indeed, Erickson [3] noted that 35% of all reported cases of SETTLE had one metastasis during their course, whereas Cheuk [4] noted a significant metastatic rate of 71% for patients with more than 5 years of follow-up after diagnosis. Metastatic disease has also been described up to 22 and 25 years after the initial operative intervention [5,6].…”

“…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.…”

“…The natural history of this disease is unclear because of the small number of cases reported in the literature and the short observation time of these patients. Although originally considered to be an indolent tumor with the potential for late blood borne metastasis, recent reports have described cases with rapid disease progression, distant metastases present at initial diagnosis, and cases occurring late in adulthood [2][3][4][5][6]. We report a case series of 3 patients with SETTLE, focusing on the clinical and pathologic features of this rare tumor, including one patient with late lung metastases who received chemotherapy with a partial response.…”

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).…”

Spindle Epithelial Tumor with Thymus-Like Differentiation: A Case Report and Review of Literature

“…Erickson et al [29 ]noted that 35% of all reported cases of SETTLE had one metastasis during their course, whereas Cheuk et al [7 ]noted a significant metastatic rate of 71%.The preferential site of metastasis is the lung, along with the cervical lymph nodes and the kidney. There are no existing guidelines regarding the treatment and follow-up of cases due to a paucity of data about the management of SETTLE tumor.…”