To identify endogenous genetic determinants that may limit Notch-driven tumourigenesis in vivo, we carried out an unbiased (genome-wide) gain-of-expression screen for loci that converted Dl-induced mild eye overgrowth into severe overgrowths (benign tumour-like growth: eye tissue is overgrown and folded) or metastatic tumours (provoke secondary eye growths throughout the body). This evidence concerns the gene EDAR and metastatic neoplasm.