Demonstration of effective antitumor immunity in an autochthonous host bearing primary colon tumors induced by 1,2-dimethylhydrazine dihydrochloride.

The role of host defense mechanisms in preventing the development of subclinical tumors into invasive tumors in an autochithonous host was studied in a model of rat colon carcinoma induced by 1,2-dimethylhydrazine dihydrochloride (DMH). Multiple gastrointestinal (GI) tumors were induced in inbred WF female rats exposed to DMH. In vitro and in vivo data suggested that the excision of the "first" GI tumor induced specific antitumor immune responses. After a complete excision of the first GI tumor, only 2 additional GI tumors were observed in 10 rats, whereas 13 and 12 additional GI tumors in 10 and 9 rats, respectively, were observed if the first GI tumor was left in situ or permitted to grow in an isolated segment of the colon. Furthermore, immunosuppression with antithymocyte globulin decreased the effectiveness of antitumor immunity induced by the immunizing first GI tumor. These experiments supported the view that an effective antitumor immunity is induced against successive tumors of an organ after a complete excision of a tumor originating in the same organ. The results of these experiments are discussed in relation to the observations of multiple primary neoplasms in humans.