Expression of toll-like receptors in recurrent pleomorphic adenoma and carcinoma ex pleomorphic adenoma

Pleomorphic adenoma (PA) is a benign salivary gland tumour that may recur or undergo malignant transformation (CXPA). Toll-like receptors (TLR) mediate immune responses triggered by various agents such as viruses and are related to tumour formation either by stimulating or suppressing their growth, with variation across different tumour entities. We compared TLR immunohistochemical expression in PA, its recurrent counterparts and CXPA and evaluated the effect of virus presence in these tumours. We studied the expression of TLR-2, -3, -5, -7 and -9 in 25 PA, 34 recurrent PA and 15 CXPA tumour samples. In addition, we examined the TLR expression levels in the presence and absence of herpes-, polyoma- and parvovirus DNA in a subset of tumours (n = 20). CXPA expressed significantly more TLR-5 and TLR-9 in the nucleus, cytoplasm and cell membrane compared with benign PA. The presence of virus DNA did not notably affect the TLR expression. TLR expression patterns seem to reflect tumour behaviour but are independent of the presence of viruses tested in this study.