Collision tumor of a malignant fibrous histiocytoma and a pleomorphic adenoma in the parotid gland: A case report

Abstract

We report a rare case of collision tumor comprising a pleomorphic adenoma and a sarcoma, pathologically diagnosed as a malignant histiocytoma, in the parotid gland.A 57-year-old Japanese woman presented with rapid swelling of the left cheek in March 2002. After the malignancy was detected by aspiration biopsy cytology in the buccal region, it was resected via surgery. Based on histopathological and immunohistochemical examinations, the postoperative diagnosis was a collision tumor comprising a malignant histiocytoma and a pleomorphic adenoma. At pathological diagnosis of the surgical specimen, the tumor was enveloped in normal tissue. The tumor recurred and was treated with radiotherapy. However, it was persistent and subsequently metastasized to the lung. Chemotherapy was delivered, but the patient died from multiple organ failure in October 2002.In the pathological finding of this sarcoma, histiocytic cells, giant cells, and multinucleated giant cells with severe atypism were regularly distributed, with thin epithelium and fibrous composition. This finding led to a malignant fibrous histiocytoma subtype diagnosis. However, this sarcoma was neither clinically nor histopathologically a typical malignant fibrous histiocytoma. Therefore, we suggest that it was either an undifferentiated high-grade pleomorphic sarcoma or a carcinosarcoma with osteoclast-like giant cells.