We hypothesized that either tumour size or genetic determinants will regulate the expression of HIF1a and set out to investigate which tumour characteristics determine the expression levels of this molecule and its regulator VHL, using a set of patients from the Leiden University Medical Center (LUMC, Leiden, the Netherlands), and subsequently corroborated our findings using data from the Cancer Genome Atlas (TCGA). This evidence concerns the gene VHL and neoplasm.