The fact that vimentin is strongly expressed in these tumours has led investigators to suggest they have an undifferentiated mesenchymal origin.4 Expression of GLUT1 in CNS hemangioblastoma has been reported to be helpful for differential diagnosis with metastatic RCC, as is the strong endothelial staining observed with most hemangioblastomas, unlike RCC, which does not show such a staining pattern.28 However, this finding is controversial, as some authors29 doubt the low specificity and tendency for high background staining. The gene discussed is VIM; the disease is renal cell carcinoma.