Equal numbers of GFP-CD133(+) (left) and DsRed-CD133(−) (middle) melanoma cells were then mixed (Figure 1a) and subsequently subcutaneously injected into athymic nude mice; tumor growth was monitored over 8 weeks using a MaestroTM in vivo fluorescent imaging system (CRI, Inc., Hopkinton, MA, USA). The gene discussed is PROM1; the disease is melanoma.