Outcome of Thyroid Carcinoma Showing Thymus-Like Differentiation in Patients Undergoing Radical Resection

Carcinoma showing thymus-like differentiation (CASTLE) is a rare malignant tumor of the thyroid. It is difficult to diagnose, and there is no universally recognized therapeutic regimen. This study aims to define the clinicopathological features and discuss the optimal management of CASTLE. We retrospectively analyzed six patients with CASTLE who accepted surgery at the First Hospital of China Medical University between January 2010 and December 2015. The six patients (three women and three men) had median age of 53 years (range 47-61 years). All patients presented with a slow-growing, painless neck mass; three patients also had hoarseness. All tumors were located in middle-lower or lower lobe, and two tumors extended to the substernal region. All patients underwent radical surgery without postoperative radiotherapy or chemotherapy. Five patients had extrathyroidal extension and two had lymph node metastasis. All six tumors were positive for CD5 and negative for thyroglobulin (Tg) and thyroid transcription factor (TTF)-1. Median follow-up was 32 months (range 23-81 months). Lateral cervical lymph node metastasis occurred in one patient at 26 months after initial treatment. CASTLE is a rare, aggressive malignant tumor of the thyroid. Ultrasound, computed tomography, and fine-needle aspiration biopsy may not be sufficient to establish the diagnosis preoperatively; pathological examination and immunohistochemistry, particularly positive CD5 staining, are necessary to establish the diagnosis. Patients with CASTLE can yield a favorable outcome after radical surgery.