S100A9 and skin squamous cell carcinoma: Ultimately, five genes—Alcohol Dehydrogenase 1B (ADH1B), C-C Motif Chemokine Ligand 27 (CCL27), Inhibitor of DNA Binding 4 (ID4), LDL Receptor Related Protein 4 (LRP4) and S100 Calcium Binding Protein A9 (S100A9)—were identified as characteristic genes of cSCC.