Thyroid Malignancies With Thymic Differentiation: Outcomes of Rare SETTLE and CASTLE Tumors

Abstract

BackgroundSpindle epithelial tumors with thymus‐like differentiation (SETTLE) and carcinomas showing thymus‐like differentiation (CASTLE) are rare intrathyroid tumors.MethodsThis retrospective cohort study included patients diagnosed with SETTLE, CASTLE, and papillary thyroid carcinoma (PTC) from 2004 to 2020 within the National Cancer Database (NCDB). Demographic, tumor, and treatment characteristics were compared. Overall survival (OS) was analyzed using the Kaplan–Meier method and Cox regression models.ResultsThis study identified 19 patients with CASTLE, 11 with SETTLE, and 483 474 with PTC. CASTLE and SETTLE patients had larger tumors, lymphovascular invasion, and positive surgical margins. They were rarely treated with radioactive iodine treatment but frequently received external beam radiation and chemotherapy. Five‐year OS was significantly lower for CASTLE and SETTLE compared to PTC. SETTLE was associated with an increased risk of death.ConclusionSETTLE and CASTLE are rare intrathyroid tumors with worse survival compared to PTC, often managed with radiation, chemotherapy, and surgery.