Cell proliferation in salivary gland tumors

Salivary gland tumors often pose considerable difficulty in differential diagnostic and prognostic assessment based on histomorphologic grounds alone. Histomorphology may poorly correlate with clinical outcome and the tumors within the same type in classification schedule exhibit different clinical courses. Prognostic relevance of various cell proliferation markers has been investigated in many types of human cancer, recently including salivary gland tumors. Evaluation of DNA content by flow cytometry and by cytophotometry, AgNOR technique, and immunohistochemical detection of antigens in cycling cells such as the Ki67 antigen and proliferating cell nuclear antigen (PCNA) have been applied to a variety of benign and malignant salivary gland tumors in only few studies so far. Cell proliferation, assessed with the MIB1 antibody, that recognizes the Ki67 antigen in proliferating cells, represents a significant prognostic factor for acinic cell carcinomas and mucoepidermoid carcinomas of salivary gland origin. Moreover, much lower proliferative activity as assessed with the MIB1 antibody helps to distinguish difficult cases of polymorphous low grade adenocarcinomas from adenoid cystic carcinomas and may contribute to differentiation of solid myoepithelial cell-rich pleomorphic adenomas from various malignant tumors. Thus, assessment of cell proliferation in salivary gland tumors using the MIB1 antibody and PCNA in paraffin-embedded tissue should be incorporated into routine immunohistologic evaluation of histologically difficult cases of salivary gland tumors.