Constitutive (HO-2) and inducible (HO-1) haem oxygenase in pleomorphic adenomas of the human parotid: an immunocytochemical study.

This study examines the expression HO-1 and HO-2 isozymes in human parotid pleomorphic adenomas. They are members of the heat shock protein family, and are thought to play a role in the regulation of tumoral blood flow. Immunocytochemistry using antibodies specific for HO-1 and HO-2 were undertaken in 12 pleomorphic adenoma specimens, all sections of which contained adjacent normal salivary tissue. Normal salivary gland acini and ducts displayed significantly stronger immunoreactivity for HO-2 compared to tumour cells (p < 0.001). Expression for HO-1 was minimal in both normal salivary gland acini and tumour cells with no difference (p = 1.000). However, positive staining for HO-1 was seen in normal salivary ducts and in pleomorphic adenomas showing ductal differentiation. In conclusion, this is the first study to examine the expression of HO-1 and HO-2 within normal salivary glands and pleomorphic adenomas. Our findings suggest that HO may be implicated in the pathogenesis of salivary pleomorphic adenomas.