Fractalkine (CX3CL1) and fractalkine receptor (CX3CR1) in squamous cell carcinoma of the tongue: markers of nerve invasion?

PURPOSE: Perineural invasion (PNI) in oral squamous cell carcinoma (SCC) is an independent predictor of poor prognosis. As PNI is not always identified with routine histology, a surrogate marker of PNI would improve detection and better inform treatment planning. The chemokines fractalkine (CX3CL1) and its receptor (CX3CR1) have shown such potential in other cancers, but have yet to be investigated with respect to PNI in oral SCC. METHODS: Thirty SCCs of the tongue in which PNI was identified histologically, and 30 in which it was not, were stained for fractalkine and fractalkine receptor using polyclonal antibodies and an immunoperoxidase technique. Tumours were assessed as either positive or negative; no attempt was made to subjectively assess staining intensity or extent. RESULTS: Both markers labelled myofibroblasts in the stroma surrounding the tumour, various neural components, leucocytes, endothelium and salivary myoepithelial cells. Fractalkine also labelled salivary ductal epithelium, vascular smooth muscle and 12/30 SCC which showed PNI. Eight of 30 positive SCCs in which PNI was not identified were also positive for this marker. There was no statistically significant association between fractalkine staining and PNI (p = 0.273). No SCC was positive for fractalkine receptor, but immune dendritic cells within tumour islands were strongly positive, as was striated muscle. CONCLUSIONS: Neither fractalkine nor fractalkine receptor is a reliable surrogate marker of PNI in lingual SCC.