However, although the tumor spectrum associated with p53 inactivation was remarkably different in Trp53-heterozygous mice, our previous skeletal analysis of 12-month-old Trp53+/- animals revealed that osteosarcoma development was only detectable, when the gene encoding the protein tyrosine phosphatase Rptpζ was deleted simultaneously [4]. The gene discussed is TP53; the disease is osteosarcoma.