Chemoimmunotherapy of a murine fibrosarcoma: critical factors for success of combined modality therapy.

Thiabendazole (TBZ), a new nonspecific immunopotentiator, was evaluated in combination with Cytoxan in the therapy of a syngeneic murine fibrosarcoma. The reduction of tumor burden by chemotherapy was critical in achieving an optimal response from immunotherapy. Eighty-eight percent of the mice that responded to Cytoxan had sustained regression of tumor with TBZ treatment. The response to TBZ was markedly diminished, both in duration and magnitude, in the mice considered to be Cytoxan nonresponders. Timing of immunotherapy was also important. If Cytoxan and TBZ were given simultaneously, growth kinetics similar to those observed with Cytoxan alone were observed. However, if TBZ was given 4 days after Cytozan administration, prolonged regression of tumor was seen. Alone, TBZ was most effective at a dose of 20 mg/kg. However, in combination with Cytoxan the most effective dose was 0.2 mg/kg. The implications of this finding are discussed.