Metastasizing Pleomorphic Adenoma with Myoepithelial Cell Predominance

The biological behavior of pleomorphic adenomas (mixed tumors) of salivary gland origin is complex. Tumors with benign histologic features may exhibit recurrence and locally aggressive behavior especially after incomplete excision. A small percentage of pleomorphic adenomas have obvious malignant components in epithelial or in both epithelial and mesenchymal components and can metastasize. There are also rare case reports which appear to document typical pleomorphic adenomas of salivary gland with histologically identical visceral and lymph node metastases. Recently myoepithelial cell proliferation has been identified as a possible predictor of aggressive clinical behavior in otherwise histologically benign pleomorphic adenomas. We report such a parotid gland lesion with local recurrence and retroperitoneal spread. DNA-flow cytometry of cells from the paraffin-embedded primary and metastasis showed similar aneuploid populations. Aneuploidy appeared to reflect the malignant potential of this particular pleomorphic adenoma and suggests that DNA-flow cytometry of salivary gland tumors may yield important prognostic information.