Effective tumor chemotherapy requires targeting the anticancer drug to tumor cells and its molecular sites of action.Systemic administration and non-targeted distribution of the drug within the living system reduces therapeutic efficacy and,simultaneously increases the risks of undesirable side effects and toxicity.Thus,selective delivery of cytotoxic drugs to tumor cells may strongly decrease undesirable side effects of antineoplastic agents.To achieve this goal in cancer therapy,a promising method may involve drugs covalently conjugated to macromolecular carriers.