Our study uses a non-orthotopic tumor mouse model to show that tumor cells in areas far from blood vessels where PgP inhibitors have no effect (or possibly even a negative effect) due to changes in distribution of doxorubicin, might counterbalance areas close to blood vessels where uptake of doxorubicin into tumor cells is increased, thus limiting the effectiveness of these inhibitors. The gene discussed is PGP; the disease is neoplasm.