Expression of nitric oxide synthase in pleomorphic adenomas of the parotid

The actions of nitric oxide (NO) in the pathology of solid tumours are complicated and many are poorly understood because NO has both inhibitory and tumour-promoting activities. In the current study we aimed to find out immunohistochemically whether the expression of both the inducible (iNOS) and endothelial (eNOS) forms of the enzyme nitric oxide synthase (NOS) were changed in pleomorphic adenomas of the parotid compared with normal salivary tissue. There was a significant difference in staining for iNOS between the tumour and normal salivary tissue, with tumour epithelial cells being stained in 29 cases of the 30 cases studied (P < 0.0001). The luminal cells of the salivary ducts also stained, but not the normal salivary tissue. Immunohistochemistry for the eNOS isoenzyme showed moderate staining of the tumour epithelium in only three specimens. There was also mild staining in the salivary duct cells of the normal glandular tissue and in endothelium of blood vessels in both tumour and normal glandular tissue in the same 29 cases.