Disclosed is an agent which has a destructive effect on malignant tumors and contains alpha-ketoglutaric acid, N-acetyl-seleno-L-methionine, N-acetyl-L-methionine, and a compound that is capable of forming azomethine and is selected among the group 5-hydroxymethylfurfural, dehydroascorbic acid, maltol, and vanillin as an active substance, 5-hydroxymethylfurfural being preferred. The inventive agent can be used in the form of an infusion, in an oral or rectal form of administration, or as an irrigation in cancer therapy.