Metastatic Mixed Tumor Arising in Bone
A Case Report and Review of the Literature
Richard L. McGough, MD; Li Juan Wang, MD; Douglas R. Gnepp, MD; Richard M. Terek, MD

Mixed tumors, or pleomorphic adenomas, are the most common benign tumors of the salivary gland1. Minsen2 first described them in 1874 as heterogeneous tumors of the parotid gland containing both mesenchymal and epithelial features3. An entity known as benign metastasizing mixed tumor has also been described4,5. It occurs when a histologically benign mixed tumor metastasizes to other sites, such as soft tissue, the liver, and bone4-7. Rarely, malignant mixed tumors arise in extrasalivary locations, including bone4,8. We know of one case report in which a mixed tumor with malignant characteristics arose in bone and metastasized to the lungs9. We report the first case that we are aware of in which a histologically benign mixed tumor arising in bone metastasized to the lungs. Histologic examination of the metastatic lesion revealed tissue identical to the primary lesion, with no evidence of malignant degeneration.

Case Report

A forty-two-year-old woman presented in 1995 with a left pretibial mass. No systemic symptoms were noted at that time. Radiographs revealed a lytic lesion in the proximal part of the tibia (Fig. 1-A). A computed tomographic scan demonstrated the lytic lesion eroding the anterior tibial cortex, with no internal characteristics (Fig. 1-B). A bone scan showed increased activity in the proximal part of the tibia and no other osseous lesions (Fig. 1-C). Open biopsy was performed, followed by curettage and packing with methylmethacrylate (Fig. 1-D). Pathologic examination revealed a mixed tumor with an entirely benign histologic appearance, and consultation with two bone pathologists confirmed the benign nature of the lesion. Evaluation of the head and neck for evidence of a primary tumor consisted of a computed tomographic scan of the neck, direct laryngoscopy, and examination by an otolaryngologist. There was …


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