MYCN and neoplasm: Thus, should the contribution of tumour cell-derived microvessels be confirmed in human NB primary tumours, as our preliminary findings with MYCN amplified NB tumours seem to indicate (Pezzolo et al, unpublished), NB xenografts made up of mixed murine- and tumour-derived endothelial cells may prove useful for the testing of the therapeutic activity of antiangiogenic compounds.