Cytologic findings of spindle epithelial tumor with thymus-like elements

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.

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.