Abstract: The presence of tumor nodules in organs often results in serious clinical manifestations and the permeation by cancer cells of sheaths surrounding organs often produces clinical manifestations of pleural effusion, ascites or cerebral edema. The present invention addresses this problem by providing a method for treating tumors comprising (a) intratumoral administration of a superantigen and/or (b) intrathecal or intracavitary administration of a superantigen directly into the sheath. Intratumoral superantigen results in significant and sustained reduction of the tumor size. Intrathecal administration produces significant sustained reduction of the fluid accumulation associated with clinical improvement and prolonged survival. Useful superantigen compositions for intrathecal and intratumoral injection include tumoricidally effective homologues, fragments and fusion proteins of native superantigens.