Malignant rhabdoid tumor arising from a pleomorphic adenoma

Malignant transformation of pleomorphic adenomas often occurs in long-standing tumors or tumors with multiple local recurrences. The malignant component is usually a carcinoma. The case reported herein concerns a 60-year-old man who had a malignant rhabdoid tumor arising in a painless parotid mass that remained untreated for 25 years. Malignant rhabdoid tumors are clinically aggressive neoplasms with phenotypic features that resemble rhabdomyomatous differentiation but lack genuine skeletal muscle differentiation. The salient features of rhabdoid tumor cell include large, pleomorphic, and eccentric nucleus and a solitary and prominent intracytoplasmic inclusion that is strongly immunoreactive for vimentin. It is our understanding that this is the first reported case of malignant rhabdoid tumor arising in the parotid gland in the English literature. The pathologic features of our case will be discussed in context with malignant rhabdoid tumors from other parts of the body.