A Rare Osteoid Forming Carcinosarcoma Ex‐Pleomorphic Adenoma of the Parotid Gland

Salivary gland carcinosarcoma is a combination of malignant epithelial and sarcomatous tumors and can develop from a preexisting pleomorphic adenoma or de novo. These tumors are rapidly growing infiltrative tumors and have an extremely poor prognosis, with a high frequency of lymphatic and hematogenous spread at the time of diagnosis. Approximately half of the cases of carcinosarcoma arise from preexisting pleomorphic adenoma with a long-standing clinical history of parotid mass. The carcinomatous component is most commonly squamous cell carcinoma or adenocarcinoma, while chondrosarcoma is the most frequent sarcomatous component. Our case is particularly unusual due to the presence of osteosarcomatous differentiation as the sarcomatous component. In addition to its histological rarity, our patient has never been reported a prior parotid mass or history of pleomorphic adenoma in this location. However, thorough examination of the radical parotidectomy specimen revealed sclerosed foci of pleomorphic adenoma in addition to carcinosarcoma with osteoid formation. In conclusion, we report an unusual case of carcinosarcoma ex-pleomorphic adenoma with osteoid formation and osteoclast giant cells in a patient without a history of pleomorphic adenoma or parotid mass.