After the administration of metformin in combination with the conventional protocol including cyclophosphamide, doxorubicin hydrochloride (hydroxydaunorubicin), vincristine sulphate, and prednisone, canine patients with recurrent DR lymphomas showed decreased MDR proteins comparable to those that were found to be elevated in many cases of MDR cancers in humans, including MDR-1. This evidence concerns the gene ABCB1 and lymphoma.