Treatment of rat fibrosarcoma by radiotherapy plus immune adjuvant.

Combined radiotherapy and nonspecific adjuvant C. parvum or Piromen treatment of rat tumors show improvement over radiotherapy alone. The most effective protocol, resulting in complete remission in 6 of 6 rats was obtained with C. parvum given i.p. in three doses 1 day prior to tumor X-irradiation of three doses of 1500 R each given on days 1, 4, and 8. Animals receiving the same dose schedule without adjuvant had only partial regression of their tumor. Without adjuvant, increasing the dose to 6000 R also resulted in tumor regression, but at the expense of marked necrosis to the leg. One mechanism for the observed results may be stimulation of the reticulo-endothelial system to produce macrophages activated against the tumor. It is also possible that C. parvum causes increased rate of clearance of soluble antigens released as a result of radiation destruction of the tumor, as suggested by Proctor et al (3).