Spindle epithelial tumor with thymus-like differentiation (SETTLE): clinical-pathological features, differential pathological diagnosis and therapy

Abstract

Spindle epithelial tumor with thymus-like differentiation (SETTLE) is a very rare tumor of the thyroid gland. An algorithm for the diagnosis and treatment of SETTLE has yet to be established. The aim of this study was to identify all case reports of SETTLE and to compare the clinical-pathological features and therapy of the cases identified. We performed a PubMed search for case reports of SETTLE in English published up to November 2014 in which "SETTLE" and "Spindle epithelial tumor with thymus-like differentiation" were keywords. We identified 35 articles for a total of 42 cases. We found that SETTLE usually occurs in children and adolescents as an asymptomatic neck mass. Thyroid function tests and tumor markers are invariably within normal range in all patients, and fine needle aspiration biopsy is rarely diagnostic for SETTLE. All 42 patients had undergone thyroidectomy. After surgical resection, chemotherapy (adjuvant or first/second-line treatment) and/or radiotherapy were administered to control tumor growth in cases with metastatic involvement. Although SETTLE presents a low-grade malignancy, it can metastasize to lymph nodes, the mediastinum, lung, vertebrae, and kidney even many years after the initial diagnosis. SETTLE may have a good prognosis if appropriately treated at initial presentation and if patients undergo long-term monitoring with regular clinical and morphological evaluations.

Spindle epithelial tumour with thymus‐like elements presenting with lymph node metastasis: An illustrative case report with review of literature

“…The differential diagnoses include SS, ectopic spindle cell thymoma, variants of papillary thyroid carcinoma with spindle cell component such as the cribriform‐morular variant, spindle cell variant of medullary carcinoma of thyroid, sarcomatoid anaplastic carcinoma of thyroid, and solitary fibrous tumour, most of which are easily distinguished on careful review of histology and immunohistochemistry . Ectopic cervical thymoma occurs in older patients, and is usually extra‐thyroidal.…”

“…However, they express CD20, and ~80% harbour GTF2I mutations, both of which were absent in our case. SS is of higher nuclear grade, lacks diffuse expression of HMWCKs/p40/p63 or SMA as in SETTLE, and harbours X:18 translocations …”

“…Formally recognised as a distinct tumour entity in 1991, ~50 cases of spindle epithelial tumour with thymus‐like elements (SETTLE) have been reported since . Hypothesised to arise from remnants of the fourth and fifth branchial pouches with differentiation along the thymic line, SETTLE usually presents as a solitary, non‐functional, intrathyroidal mass in children and young adults . Conservative surgical resection is the treatment of choice, and the 5‐year overall survival rate is good (~75%) .…”

Cytologic findings of spindle epithelial tumor with thymus‐like elements

“…Most patients present with painless thyroid enlargement for several years prior to diagnosis. Ippolito et al recently reviewed 42 SETTLE cases and found that all patients had normal thyroid function tests and serum calcitonin and carcinoembryonic antigen levels. Radiographic imaging has not been well characterized, but a heterogeneous solid‐cystic pattern and cold thyroid scans have been reported .…”

“…Ippolito et al recently reviewed 42 SETTLE cases and found that all patients had normal thyroid function tests and serum calcitonin and carcinoembryonic antigen levels. Radiographic imaging has not been well characterized, but a heterogeneous solid‐cystic pattern and cold thyroid scans have been reported . Surgical resection (usually hemithyroidectomy) is the primary treatment; a few cases have documented good responses to chemotherapy and/or radiation.…”