"A method for treating solid tumors comprising the steps of preparing a pharmaceutically active composition containing a quassinoid represented by the formula ##STR28## wherein R1 represents hydrogen, oxygen, alkyl, alkenyl, acyl, aryl, halogen, sulfo, nitro, carboxyl, hydroxyl, hydroxyalkyl, alkoxy, or other water soluble sidechain, and Y is a sidechain comprising hydrogen, oxygen, halogen, hydrox" . . . .