This suggests the hypothesis that the more drug-sensitive Eμ-myc Arf-/- cells maintain better oxygenation at the expense of higher drug sensitivity by growing less compactly in the interior of the tumor – where there would be stronger competition for oxygen and cell nutrients – whereas the Eμ-myc p53-/- lymphoma cells may enhance their survival by closer packing in the core of the tumor. This evidence concerns the gene TP53 and lymphoma.