We found a striking heterogeneity in the expression of these genes: median expression of the gene XDH showed the most striking heterogeneity with some tumours expressing negligible levels of XDH (for example, glioma and glioblastoma) while others were characterised by high XDH expression levels (PAAD, HCC and HNSCC). The gene discussed is XDH; the disease is head and neck squamous cell carcinoma.