Two differentially expressed genes were selected for in-vivo validation, Aldh3a1 and Id2. Downregulation of either gene resulted in reduced tumour burden following intracranial inoculation whereas ectopic expression in either mouse or human tumour cells resulted in increased metastatic burden in the brain following intracardiac inoculation but did not promote increased metastasis to the lung. This evidence concerns the gene ID2 and neoplasm.