We next inoculated immunodeficient (NOD.Cg-Prkdcscid, Il2rdtm1Wjl/SzJ) mice with fl/fl Pdgfrb and Δ/Δ Pdgfrb primary tumor cells at low (1 × 105) and ten-fold higher (1 × 106) densities and monitored tumor initiation and development over time. The gene discussed is PDGFRB; the disease is neoplasm.