Podoplanin expression in tumor-free resection margins of oral squamous cell carcinomas: an immunohistochemical and fractal analysis study

Podoplanin is involved in tumorigenesis and cancer progression in head and neck malignancies and its expression is not restricted to lymphatic vessel endothelium. The aim of this study was to establish podoplanin expression in the tumor-free resection margins of oral squamous cell carcinomas (OSCCs) and to evaluate the geometric complexity of the lymphatic vessels in oral mucosa by utilizing fractal analysis. As concerns the podoplanin expression in noncancerous tissue, forty tumor-free resection margins from OSCCs were investigated utilizing immunohistochemistry for D2-40 antibody and image densitometry analysis. Podoplanin expression was extremely low in basal cells, especially in resection margins of OSCCs developed in the lower lip regions. However, a highly variable D2-40 expression in tumor-free resection margins associated with hyperplastic or dysplastic lesions was identified. Moreover, podoplanin expression also extended to the basal layer of the lower lip skin appendages, the myoepithelial cells of acini and ducts of minor salivary glands, and other structures from the oral cavity. As concerns the study of the density and complexity of oral lymphatic vessels architecture by means of immunohistochemistry (D2-40, CD31 and Ki-67 antibodies) and fractal analysis, we demonstrated that in normal oral mucosa the geometry of the lymphatic vessels was less complex at the level of the lower lip compared to the anterior part of the oral floor mucosa or the tongue. A comparative analysis between the normal and pathological aspects revealed statistically significant differences between the fractal dimension (FD) of the vessels' outline, especially in the tongue. Fractal analysis proved an increasing lymphatic network complexity from normal to premalignant oral mucosal lesions, providing additional prognostic information in oral malignant tumors.