Cell proliferation in salivary gland adenocarcinomas with myoepithelial participation - A study of 78 cases

We used three markers of cell proliferation mitotic counts, mitotic index and expression of proliferating cell nuclear antigen - to assess the proliferative activity of a series of 78 low-grade salivary adenocarcinomas with myoepithelial participation classified according to: their histological type, the predominant architectural type, and the predominant cytological type. The series included adenoid cystic carcinomas (40), epithelial-myoepithelial carcinomas (19), polymorphous low-grade adenocarcinomas (12) and basal cell adenocarcinomas (7). The proliferation indicators were found to be similar in the first three groups, being significantly lower than in the last. Tumours formed by basal cells had statistically significant higher mitotic indexes than those predominantly composed of clear cells of myoepithelial type and ductal cells. Tubular rumours, irrespective of the histological classification of the neoplasm, had proliferation indexes similar to those found in cribriform neoplasms. Solid tumours, whether formed by ductal or clear myoepithelial-type cells, had higher indexes than the neoplasms with differentiated (cribriform and tubular) patterns. The highest mean values for every proliferation indicator used were found in tumours with solid organization that were predominantly formed by basal cells. These results agree with the hypothesis that cell proliferation is inversely related to neoplastic differentiation. The identification of the prevalent cell phenotype and architecture may extend our knowledge from adenoid cystic carcinoma, whose solid variant carries a worse prognosis, and supports that the usual classification of this group of salivary adenocarcinomas would benefit to be complemented with information on tumour architecture and cellular composition.