Among
salivary gland neoplasms are a group of rare
tumors that are histologically identical to benign mixed
tumors that inexplicably metastasize; they have been called metastasizing mixed
tumor (MZMT) of salivary glands. We report the clinicopathologic features and flow cytometric findings for 11 cases of MZMT. At the time of discovery of metastatic disease, the patients, six women and five men, ranged in age from 20 to 83 years. Primary sites of involvement included the parotid gland (eight cases), submandibular gland (two cases), and the nasal septum (one case). With one exception, all the patients had at least a single recurrences of their primary mixed
tumor, but two or more recurrences were the norm before development of metastatic foci. The
metastases were discovered from six to 52 years following the occurrence of the primary
tumor. Metastatic deposits were identified in bone, lung, regional lymph nodes, skin, kidney, retroperitoneum, oral cavity, pharynx, calvarium, and central nervous system. The
metastases either occurred simultaneously with an episode of recurrent mixed
tumor (n = 5) or from 5 to 29 years after a recurrence (n = 6). The treatment of the primary, recurrent, and metastatic
neoplasms was surgical excision. Follow-up, ranging from 8 months to 16 years following the diagnosis of MZMT, revealed seven patients to be alive without disease (64%) and two dead of causes unrelated to metastatic disease (18%). Two patients (18%) died as a direct result of metastatic
tumor at 3 and 2 years after
metastasis of their mixed
tumors. Flow cytometric analysis revealed a diploid
DNA cell population in the primary and/or metastatic
tumors in nine cases.
Aneuploid DNA cell content was identified in two of the cases.
DNA ploidy levels and cell proliferation rates were compared with those of conventional benign mixed
tumors and also with
malignant mixed tumors. Retrospective analysis of histologic parameters (mitotic rate, cellular pleomorphism, infiltrative growth, vascular or lymphatic invasion) and flow cytometric analysis failed to identify criteria to predict the development of
metastasis in these
neoplasms.