Spindle Epithelial Tumor With Thymus-Like Elements: A Case Report

TL;DR

A rare tumor called SETTLE in children's thyroids is reported, highlighting its diagnostic challenges and poor prognosis despite treatment.

Contribution

This case report adds to the limited literature on SETTLE, emphasizing the need for improved diagnostic awareness and treatment strategies.

Findings

SETTLE was diagnosed in a child with thyroid swelling through histology and molecular analysis.

The patient died due to local recurrence and lung metastases despite initial surgical treatment.

SETTLE is a rare thyroid neoplasm requiring early diagnosis and multidisciplinary management.

Abstract

Spindle epithelial tumor with thymus-like elements (SETTLE) presents as a neck swelling in children and adolescents. It is a rare malignant neoplasm derived from ectopic thymus or branchial pouch derivatives. It has a propensity for late hematogenous metastasis. Morphologically, it is a biphasic tumor composed of fascicles of spindle cells and epithelial components in the tubulo-papillary pattern. Due to its rarity, pathologists often misdiagnose it. Synovial sarcoma is its main morphologic mimic, but SETTLE lacks t(X;18) translocation. Surgery is the mainstay of treatment. Radiotherapy can be offered for local recurrence and chemotherapy for distant metastases. We report a case of gradually increasing left thyroid swelling in a boy from Pakistan. His thyroid function tests were normal. Cytology showed a spindle cell lesion, Bethesda category 5. The patient underwent a total thyroidectomy. The left thyroid lobe showed a partially encapsulated, tan-white, firm, homogenous nodule. Histology showed an encapsulated, focally infiltrating tumor, composed of spindle and epithelial cells in lobules with mild atypia. Based on immunohistochemistry, medullary carcinoma and carcinoma with thymus-like elements (CASTLE) were ruled out. Molecular analysis for t(X;18) (p11.2; q11.2) ruled out synovial sarcoma. Therefore, the final diagnosis was SETTLE. The patient died at 42 months of follow-up due to local recurrence and lung metastases. SETTLE is a rare childhood thyroid neoplasm with late metastatic potential. Early diagnosis, surgical resection, and surveillance can ensure disease-free survival. Diagnosed cases should be reported to help formulate effective chemotherapy and radiotherapy regimens for the treatment of recurrence or metastasis.

Figures