Spindle epithelial tumor with thymus-like differentiation: A case report and comprehensive review of the literature and treatment options

Spindle epithelial tumor with thymus-like elements (SETTLE): a diagnostic challenge with distinct therapeutic implication; case report

Spindle epithelial tumor with thymus-like elements (SETTLE) is a rare malignant neoplasm of the thyroid gland which is believed to arise from intrathyroidal thymic tissue. It predominantly affects young adults and children presenting with a thyroid mass of variable duration and rarely occurs in adults. It has a high overall survival with a tendency for delayed metastasis. SETTLE is a biphasic lobulated tumor composed of spindle shaped cells along with glandular formations seen on histopathological examination. Despite its typical morphology it is commonly misdiagnosed on histopathology due to its rarity and overlapping morphology with other close mimics such as a carcinoma, synovial sarcoma and thymoma. Herein we report such a case occurring in a middle aged female presenting with a neck mass. She had an initial diagnosis of metastatic poorly differentiated squamous cell carcinoma possibly with an orophayngeal primary in view of co expression of CK, p40 and p16 on immunohistochemistry. The patient underwent surgical resection with modified neck dissection. On review at our hospital it was diagnosed as SETTLE and she remains disease free after a follow-up period of 1 year. Diligent histopathological examination espoused with a judicious panel of IHC markers in conjunction with clinicoradiological findings forms the mainstay of diagnosis. Diffuse and strong p16 immunoexpression has not been documented or evaluated in literature so far, and needs to be explored for its diagnostic utility in this rare entity.

Spindle epithelial tumor with thymus-like element (SETTLE)-Report of a rare thyroid carcinoma

Spindle epithelial tumor with thymus-like element should be included in the differential diagnosis of thyroid gland cancers, particularly in medullary carcinoma, younger patients and indolent clinical presentation, because it may influence treatment and prognosis.

Cytomorphology of monomorphic spindle epithelial tumor with thymus-like elements: A case with local recurrence after subtotal resection

Spindle epithelial tumor with thymus-like elements (SETTLE) is a rare biphasic thyroid tumor with low malignant potential that has a distinct morphology. Despite fine needle aspiration (FNA) being a common method for evaluating thyroid nodules and lymph nodes, there are limited cytologic descriptions of SETTLE in the literature due to its rarity. As a result, SETTLE is frequently underdiagnosed or misdiagnosed as medullary carcinoma, thymoma, teratoma, synovial sarcoma, or solitary fibrous tumor, among others. We present a case of a 28-year-old man with a history of a hemithyroidectomy diagnosed as SETTLE found to have a neck nodule along the strap muscle suspicious for recurrence 5 years post-surgery. The ultrasound-guided FNA cytology specimen of the neck nodule showed loosely cohesive, monomorphous ovoid to spindled cells with scant cytoplasm and nuclei with fine to granular chromatin. In addition, there were occasional clusters of cells with a papillary configuration. The tumor cells were associated with magenta, amorphous extracellular material. Immunocytochemical staining of the cell block material revealed that tumor cells were positive for p63, cytokeratin AE1/3, and CK8/18 and negative for TTF-1 and thyroglobulin. Overall, the morphological and immunocytochemical findings were consistent with a local recurrence of SETTLE. The subsequent left anterior strap mass excision revealed a 4 cm encapsulated tumor consistent with SETTLE. Because ofits rarity and low level of awareness, SETTLE poses a diagnostic and therapeutic challenge. We herein present the cytologic findings of monomorphic SETTLE and highlight the potential cytomorphologic and immunophenotypic pitfalls. We also highlight how tumors with high-risk features can be a therapeutic challenge.

When to settle for SETTLE! A lesson learned from our cases

Spindle epithelial tumor with thymic like elements (SETTLE) is a biphasic tumor composed of epithelial and spindle cell components. It is an uncommon indolent tumor arising in the thyroid gland and most commonly affects the children and young adults. This entity is mostly overlooked because of its rarity and diagnostic difficulty on morphology. We discuss two cases of SETTLE with varied presentation, diagnostic challenges and lessons learnt from them.SETTLE should be considered as a differential especially when dealing with a thyroid lesion in young and adolescent. The article discusses the histologic details and common mimickers to be borne in mind aiding in arrival at the final diagnosis on biopsy specimens.

Overview of the 2022 WHO Classification of Thyroid Neoplasms

This review summarizes the changes in the 5th edition of the WHO Classification of Endocrine and Neuroendocrine Tumors that relate to the thyroid gland. The new classification has divided thyroid tumors into several new categories that allow for a clearer understanding of the cell of origin, pathologic features (cytopathology and histopathology), molecular classification, and biological behavior. Follicular cell-derived tumors constitute the majority of thyroid neoplasms. In this new classification, they are divided into benign, low-risk, and malignant neoplasms. Benign tumors include not only follicular adenoma but also variants of adenoma that are of diagnostic and clinical significance, including the ones with papillary architecture, which are often hyperfunctional and oncocytic adenomas. For the first time, there is a detailed account of the multifocal hyperplastic/neoplastic lesions that commonly occur in the clinical setting of multinodular goiter; the term thyroid follicular nodular disease (FND) achieved consensus as the best to describe this enigmatic entity. Low-risk follicular cell-derived neoplasms include non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP), thyroid tumors of uncertain malignant potential, and hyalinizing trabecular tumor. Malignant follicular cell-derived neoplasms are stratified based on molecular profiles and aggressiveness. Papillary thyroid carcinomas (PTCs), with many morphological subtypes, represent the BRAF-like malignancies, whereas invasive encapsulated follicular variant PTC and follicular thyroid carcinoma represent the RAS-like malignancies. This new classification requires detailed subtyping of papillary microcarcinomas similar to their counterparts that exceed 1.0 cm and recommends not designating them as a subtype of PTC. The criteria of the tall cell subtype of PTC have been revisited. Cribriform-morular thyroid carcinoma is no longer classified as a subtype of PTC. The term "Hürthle cell" is discouraged, since it is a misnomer. Oncocytic carcinoma is discussed as a distinct entity with the clear recognition that it refers to oncocytic follicular cell-derived neoplasms (composed of > 75% oncocytic cells) that lack characteristic nuclear features of PTC (those would be oncocytic PTCs) and high-grade features (necrosis and ≥ 5 mitoses per 2 mm²). High-grade follicular cell-derived malignancies now include both the traditional poorly differentiated carcinoma as well as high-grade differentiated thyroid carcinomas, since both are characterized by increased mitotic activity and tumor necrosis without anaplastic histology and clinically behave in a similar manner. Anaplastic thyroid carcinoma remains the most undifferentiated form; squamous cell carcinoma of the thyroid is now considered as a subtype of anaplastic carcinoma. Medullary thyroid carcinomas derived from thyroid C cells retain their distinct section, and there is a separate section for mixed tumors composed of both C cells and any follicular cell-derived malignancy. A grading system for medullary thyroid carcinomas is also introduced based on mitotic count, tumor necrosis, and Ki67 labeling index. A number of unusual neoplasms that occur in the thyroid have been placed into new sections based on their cytogenesis. Mucoepidermoid carcinoma and secretory carcinoma of the salivary gland type are now included in one section classified as "salivary gland-type carcinomas of the thyroid." Thymomas, thymic carcinomas and spindle epithelial tumor with thymus-like elements are classified as "thymic tumors within the thyroid." There remain several tumors whose cell lineage is unclear, and they are listed as such; these include sclerosing mucoepidermoid carcinoma with eosinophilia and cribriform-morular thyroid carcinoma. Another important addition is thyroblastoma, an unusual embryonal tumor associated with DICER1 mutations. As in all the WHO books in the 5th edition, mesenchymal and stromal tumors, hematolymphoid neoplasms, germ cell tumors, and metastatic malignancies are discussed separately. The current classification also emphasizes the value of biomarkers that may aid diagnosis and provide prognostic information.

Spindle Epithelial Tumor with Thymus-Like Differentiation (SETTLE): A Case Report

Background: Spindle epithelial tumor with thymus-like differentiation (SETTLE) is a tumor with an indolent disease course and late metastatic potential. It occurs primarily in children and adolescents, although it can present later in life. It was first described by Chan and Rosai [Tumors of the neck showing thymic or related branchial pouch differentiation: a unifying concept. Hum Pathol. 1991;22(4):349-67. doi:10.1016/0046-8177(91)90083-2], and there have been approximately 46 cases published in the English literature. Case report: We present an 8-year-old female with a SETTLE, undergoing an initial fine-needle aspiration and later a diagnostic biopsy. There is no evidence of disease recurrence at 3.5 years of follow-up. Conclusion: Though fine-needle aspirate biopsy is useful in directing the diagnostic workup of SETTLE by indicating concerning pathology, the broad differential diagnosis associated with it requires histology in conjunction with a limited immunohistochemical panel and unremarkable cytogenetics workup. Surgical resection is the main stay of treatment, and long-term follow-up is important in these patients.

Spindle epithelial tumour with thymus-like differentiation: report of two cases

Spindle epithelial tumour with thymus-like differentiation (SETTLE) is a very rare neck malignancy arising from thymic tissue or branchial pouch, mostly seen in the early decades of life. SETTLE is thought to be a low-grade neoplasm but distant metastases have been reported. Fewer than 50 cases have been reported in the PubMed database. We report on the four-year follow-up for a 13-year-old boy, with no signs of recurrence or distant metastasis. In addition, a 45-year-old woman was admitted to hospital with neck mass. Fine-needle aspiration biopsy was compatible with medullary thyroid carcinoma but serum levels of calcitonin were normal. Total thyroidectomy and central compartment lymph node dissection was planned with an initial diagnosis of medullary thyroid carcinoma. At surgery, frozen section analysis converted our diagnosis to SETTLE and the intraoperative strategy was changed. SETTLE should be considered in a patient with normal serum calcitonin levels in the presence of suspicious medullary thyroid carcinoma at fine-needle aspiration biopsy. Frozen section analysis may help to manage the intraoperative strategy. This report describes the first case of SETTLE successfully diagnosed by frozen section analysis.

Spindle Epithelial Tumor of Thymus-like Differentiation (SETTLE) in a 3-year-old African girl

Spindle epithelial tumor with thymus-like differentiation (SETTLE) is a rare tumor of the thyroid gland occurring in children and young adults. This report presents SETTLE as a tumor that can also affect young children (under fives). Although majority of the reports were in Caucasians, the tumor can affect all races.

Spindle Epithelial Tumor with Thymus-Like Differentiation (SETTLE): A Next-Generation Sequencing Study

Spindle epithelial tumor with thymus-like differentiation (SETTLE) is a malignant biphasic neoplasm of the thyroid or neck with propensity for late metastasis. Unlike synovial sarcoma, its main morphologic mimic, SETTLE lacks synovial sarcoma-associated translocations. A single case of SETTLE has shown a KRAS mutation but to date no comprehensive next generation sequencing studies of this rare neoplasm have been undertaken. Herein, we subjected 5 well defined cases of SETTLE to direct sequence analysis of 592 genes and fusion gene analysis of 52 genes frequently rearranged in human cancers. We identified one case with two pathogenic variants in the KMT2D gene, one being in an intron splice site (c.674-1A>G) and the other being a frameshift variant (p.M2829fs). This same case also had a pathogenic nonsense variant in the KMT2C gene (p.R1237*). A second case of SETTLE carried a pathogenic NRAS missense variant, Q61R. No other molecular alterations, microsatellite instability, gene fusions or amplifications were identified.

Spindle Epithelial Tumor with Thymus-like Element (Settle): a Case Report

Spindle epithelial tumor with thymus-like element (SETTLE) is a very rare malignant neoplasm of the thyroid. It is generally encountered in children, adolescents, and young adults Objective: We aimed to present a patient with SETTLE and to review the clinical and pathologic features of this rare tumor. A 13-year-old male patient presented to our clinic with complaints of a rapidly growing lump on his neck. There was no evidence of distant metastases at time of presentation. A total thyroidectomy was performed. Lymph node dissection was not performed. On the first postoperative day, the patient was discharged uneventfully. Histopathological and immunohistochemical analysis revealed a SETTLE in our case. During 1 year of follow-up, the patient had no complaints or symptoms, without tumor recurrence on imaging studies. Although SETTLE is a very rare entity, it should be considered when diagnosing rapidly growing masses in the thyroid, especially in younger patients.

Review of the touch preparation cytology of spindle epithelial tumor with thymus-like differentiation

We experienced a case of spindle epithelial tumor with thymus-like differentiation (SETTLE) with touch preparation cytology performed during the intraoperative frozen section diagnosis in a 22-year-old woman. The tumor was partially encapsulated by fibrous capsule. It was a highly cellular biphasic tumor characterized by fasciculated spindle cells with streaming pattern and tubulopapillary epithelial component. The tumor cells were positive for cytokeratin, vimentin, c-kit, epithelial membrane antigen (EMA), and thyroid transcription factor-1 (TTF-1). However, the tumor cells were negative for thyroglobulin, calcitonin, CD99, S-100 protein, CD34, smooth muscle actin, HBME-1, and galectin-3. The reviewed touch smears showed tight clusters with high cellularity. Most cellular clusters showed papillary configuration. However, some clusters showed spindle cells with streaming pattern. The spindle tumor cells showed elongated and cigar-shaped nuclei. Although the incidence is very rare, SETLLE should be included in the differential diagnosis when a spindle cell neoplasm is encountered in touch preparation cytology in young patients with a thyroid mass.

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

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.