Abstract: The use of classical superantigens for treatment of cancer has resulted in a low response rates and serious toxicity in humans which is attributable, in part, to the presence of preformed superantigen specific antibodies in the plasma of treated patients. The present invention addresses this problem by providing a method for treating tumors comprising the administration of one or a plurality of egc (enterotoxin gene cluster) staphylococcal enterotoxins comprising staphylococcal enterotoxins G, I, M, N, O. These superantigens in native unmodified form can be administered intrathecally, intratumorally, intravenously to humans with advanced lung cancer while resolving pleural effusions and prolonging survival to 300% above control patients treated with talc pleurodesis. Intratumoral egc superantigens induces a significant and sustained reduction of the tumor size.