Primary Alveolar Soft Part Sarcoma Arising in the Thyroid Gland: A Rare Case Report

Background: Alveolar soft part sarcoma (ASPS) is a rare aggressive soft tissue sarcoma usually involving the soft tissue of thigh and buttock region in adults. In children, head and neck presentation is more common, with orbit and tongue being the preferred sites. Alveolar soft part sarcoma primarily arising in the thyroid gland is an extremely rare clinical entity, with only two other cases being reported in the literature to date. Case: A 16-year-old boy presented with respiratory distress and enlarged thyroid gland. Hemithyroidectomy revealed well-circumscribed nests of large cells with abundant eosinophilic cytoplasm arranged in a pseudoalveolar pattern and separated by fibrous septa containing sinusoidal blood vessels. The tumor cells showed nuclear positivity for TFE3 protein and the TFE3 gene rearrangement in 79% of the nuclei. The patient's most recent chest computed tomography revealed multiple subcentimeter nodules occupying the lung bases emphasizing the aggressiveness of the disease process and the need for constant surveillance.