By crossing these mice with conditional knockout mice carrying floxed alleles of the tumour suppressor genes p53 (p53loxP/loxP) and Pten (PtenloxP/loxP), we explored whether this highly selective and regionally confined targeting would modify the phenotype of tumours arising from the subventricular zone (SVZ) stem/progenitor cells. The gene discussed is PTEN; the disease is neoplasm.