Supplementary Material for: Characterisation of Prognosis and Invasion of Cutaneous Squamous Cell Carcinoma by Podoplanin and E-Cadherin Expression

Background: Around 5% of all cutaneous squamous cell carcinoma (cSCC) metastasise. Metastases usually locate in regional skin and lymph nodes, suggesting collective cancer invasion. The cellular level of tumour invasion and prognostic parameters remain to be characterised. Methods: We performed immunohistochemical analyses of E-cadherin (marker for collective cancer invasion) and podoplanin (marker for epithelial-mesenchymal transition [EMT], single-cell invasion) expression in 102 samples of metastatic and non-metastatic cSCC and 18 corresponding skin and lymph node metastases to characterise the invasion of cSCC. Immunohistochemical results were retrospectively correlated with clinical data. Results: E-cadherin was highly expressed in metastatic and non-metastatic cSCC and skin metastases. This suggests collective cancer invasion. However, E-cadherin was downregulated in poorly differentiated cSCC and lymph node metastases, suggesting partial EMT. Podoplanin was significantly upregulated in metastatic (p = 0.002) and poorly differentiated (p = 0.003) cSCC. Overexpression of podoplanin represented a statistically independent prognostic factor for disease-free survival (p = 0.014). Conclusion: Collective cancer invasion is likely in cSCC. In lymph node metastases and poorly differentiated cSCC, partial EMT is possible. Podoplanin is an independent prognostic parameter for metastasis.