A case of metastasizing pleomorphic adenoma in the maxillary bone appearing twenty years after initial resection of pleomorphic adenoma of the hard palate.

Metastasizing pleomorphic adenoma (MPA) is the inexplicable metastasis of a histologically benign pleomorphic adenoma (PA). Approximately 50 cases have been reported. A 62-year-old woman noticed pain in the upper molar area. Her medical history included an operation for PA in the hard palate that was performed 20 years previously. On imaging, four relatively well-defined lesions were demonstrated in the maxillary bone. She underwent an operation for these lesions. Each lesion revealed the same histological features. Morphological findings displayed typical features of PA. Immunohistochemical staining showed that tumor cells of both primary and metastasizing lesions were positive for pleomorphic adenoma gene (PLAG) 1, which is a sensitive marker for PA. Gene fusions involving PLAG1 were examined by reverse transcription-polymerase chain reaction. However, no gene rearrangements of PLAG1 were found. We report here on a case of MPA in the maxillary bone, which appeared 20 years after resection of the primary tumor and review the relevant literature.