This value is much lower than Vt values for tumors, that could be found in literature for animal tumor model [20], or derived from published rate constants for human and rat glioma [21, 22], reflecting lower k1/k2 ratio in normal tissues, that in turn could be explained by differences in expression of amino acid transporters, between normal and tumor cells and their affinity to the ligand. This evidence concerns the gene SLC38A7 and glioma.