In contrast to fully spliced TrkA expression, which reduces NB xenograft tumorigenicity, tumour-associated angiogenesis and angiogenesis factor expression by NB cells [44, 45], xenograft tumours formed by TrkAIII transfectants are more vascular than tumours formed by control or fully spliced TrkA transfectants [19], consistent with a more angiogenic phenotype. This evidence concerns the gene NTRK1 and neoplasm.