Alveolar soft part sarcoma presenting as a breast metastasis in a patient with a history of thyroid cancer: a case report.

Metastases to the breast are uncommon, accounting for 0.5% of breast tumors, and most of them are originated from lymphoma, melanoma and carcinomas of various organs. Alveolar soft part sarcoma (ASPS) is a very rare neoplasm that is usually found in the lower extremities. Lungs are the common site of dissemination and may represent initial manifestation of disease. We report a clinically unsuspected case of ASPS presenting as a breast metastasis in a 25-year-old woman. The patient's medical history was notable for a thyroid cancer treated by surgery and radioiodine ablation 2 years ago. Core needle biopsy of slowly growing breast mass yielded polygonal cells with abundant eosinophilic cytoplasm arranged into solid pattern. Differential diagnosis between apocrine cell carcinoma, paraganglioma, granular cell tumor, neuroendocrine carcinoma, ASPS and metastatic hepatocellular and renal cell carcinoma was rendered by immunohistochemistry. Strong nuclear TFE3 immunoreactivity confirmed a diagnosis of ASPS. Retrospectively a primary tumor was found in the thigh. Most likely, ASPS and thyroid cancer in the patient were growing synchronously and independently.