Spindle epithelial tumor with thymus-like differentiation in fine needle aspiration of thyroid gland: Report of two cases

Spindle epithelial tumor with thymus-like differentiation (SETTLE) is a rare, malignant tumor of the thyroid gland that typically affects young males and has a propensity for late metastasis. With fine needle aspiration (FNA) being a primary tool for diagnosis of thyroid lesions, there are rare reports of cytological features of SETTLE on FNA since its initial characterization 30 years ago . Here we report two cases of SETTLE, involving 9-year-old and 15-year-old male patients. Both patients underwent US-guided FNA with a subsequent resection confirming the diagnosis of SETTLE. In the first patient the thymic origin of the tumor was suspected on FNA, but the diagnosis of SETTLE was established only after resection. Five years later, this patient presented with an enlarged ipsilateral cervical lymph node. Needle biopsy confirmed it to be a metastatic tumor compatible with SETTLE. In the second patient the diagnosis of SETTLE was suggested on FNA. Cytology of the thyroid gland nodule on FNA from both patients showed loosely cohesive and single spindle-shaped epithelial cells associated with metachromatic stroma. The differential diagnosis of spindle cell lesions of the thyroid should include SETTLE based on characteristic morphological features, after more common entities of thyroid gland such as medullary carcinoma are excluded.