Drug concentration is not the only factor defining efficiency in tumor cells eradication. Drug concentration is not the only factor defining efficiency in tumor cells eradication. The diffusion of species from blood vessels to the interior of avascular tumors creates gradients of concentration that favors survival of cells further from tumor-host interface. The exposure of the tumor model to 2DG during 5,000 seconds is enough to produce energy depletion in most cells inside tumor but can only kill a fraction of cells in intermediate region if exposed to only 1,000s. This exposure time is crucial for the efficiency of a drug such as 2DG which acts mainly in inner regions of tumor.