Expression of cyclooxygenase-2, Bcl-2 and Ki-67 in pleomorphic adenoma with special reference to tumor proliferation and apoptosis.

The present report is of immunohistochemical and cell biological studies on cyclooxygenase(COX)-2, Bcl-2 and Ki-67 in pleomorphic adenoma (n = 35). Pleomorphic adenomas from oral minor glands (n = 15), parotid gland (n = 11), Submandibular gland (n = 8) were studied and sublingual gland (n = 1). Expression of COX-2, Bcl-2 and Ki-67 was examined immunohistologically. Immunostaining intensity of COX-2 and Bcl-2 was classified into expression levels from +3 to 0. The positivity to Ki-67 was evaluated by counting the number of positive cells per 1000 cells, and the values were expressed in as percentage. Apoptotic cells were detected using the modified TUNEL method. Expression of COX-2 mRNA was analyzed by real time PCR using fresh tissues of 4 cases. The relationship between morphological findings and the level of COX-2 mRNA expression was analyzed using a laser capture microdissection (LCM). The results of immunohistochemistry and gene analysis using LCM revealed expression of COX-2 mainly in luminar tumor cells. Expression of COX-2 in pleomorphic adenoma was correlated with expression of Bcl-2 statistically (p = 0.044 < 0.05, r = 0.342). There was only a small number of apoptotic cells cells, and intensity of expression of TUNEL was not correlated with the expression of COX-2 (p = 0.463 > 0.05, r = -0.128). There was no statistical correlation between COX-2 and Ki-67 (p = 0.97 > 0.05, r = -0.07). It is suggested that COX-2 may inhibit apoptosis mediating Bcl-2 expression in pleomorphic adenoma, rather than playing a role in cell proliferation.