Abstract: The present invention relates to a combined preparation that is effective against cancerous cells containing as the active substances at least one 1-diethylaminoethyl-3-quinoxalin-2-one derivative of formula wherein R1 and R2 independently of one another are hydrogen, methyl, ethyl, propyl, butyl, or R1 and R2 together are a cycloalkyl compound; R3 is methoxy, ethoxy, hydroxy, hydrogen, C1-C4 alkyl, halogen; and n=1, 2 or 3 or a pharmaceutically acceptable salt of said derivatives, and an effective quantity of a cytostatic anti-cancer drug, such as a compound from the class of oxysterols or polyphenols, or a mixture containing selenium and L-cystcine and/or L-glutathione, or a mixture containing vitamins of the B-complex, in particular with the vitamins B1 and/or B6 and/or B12, with the exception of cis- or oxaliplatin and irinotecan.