Collision tumor of the thyroid: a case report of metastatic liposarcoma plus papillary thyroid carcinoma

Abstract

BACKGROUND: The term collision tumor represents the proximal coexistence of two histologically distinct tumors. Collision tumors within the thyroid are extremely rare, and reported cases are usually of mixed histologies of papillary and medullary carcinomas. Metastatic disease to the thyroid is also an uncommon scenario but may develop after long disease-free intervals. Carcinomas, most commonly renal cell carcinoma, are the likeliest group of neoplasms to metastasize to the thyroid. Soft tissue sarcomas metastasize to the thyroid with a much lower frequency. METHODS: We are reporting this highly unusual case of metastatic liposarcoma from the thigh to thyroid, which harbored a collision tumor of papillary thyroid carcinoma. This 86-year-old woman had undergone an initial resection for liposarcoma of the thigh two decades before being seen with a thyroid mass. RESULTS: Histologically, the thyroid mass was a metastatic myxoid liposarcoma, identical to the primary neoplasm. Papillary thyroid carcinoma was present within this metastasis and in the adjacent thyroid. CONCLUSION.: For any patient seen with a thyroid mass with a history of prior malignancy, no matter how remote, metastatic disease should be considered in the differential diagnosis.