A method of preparing and using a sterile non-toxic pyrogen-free cold extract from the leaves of Nerium oleander as a supplementary medication to cancer chemo-, hormon and/or radiotherapy to restore and/or ameliorate the immune system of the patient and/or to decrease side effects and increase the antitumor effects of radiotherapy and chemotherapeutics, particularly when used in combination with taxol, adriamycin, cisplatin, 5-fluoro-uracil, alimta, cyclophosphamide, mitomycin-C, navelbine, taxotere and topotecan, respectively, and its use in the manufacture of a medicament for the treatment of one or more cancers of bladder, kidney, liver, ovary, pancreas, testicle, uterus, and vagina as well as pleuramesotheliomas and Hodgkin's lymphomas.