Autochthonous grafts of spontaneous mammary adenocarcinoma of mice give 100% takes with no spontaneous regression. However, the growth of these autografts was markedly inhibited with a high rate of complete regression when the grafts were mixed with ascitic Sarcoma 180 and implanted under i.p. treatment with lentinan. Lentinan is one of the so-called antitumor-active plant polysaccharides; it strongly inhibits Sarcoma 180 but has no effect on autochthonous grafts. Without the lentinan treatment, the mixed autografts and Sarcoma 180 or Sarcoma 180 alone constantly produced large tumors. These results indicate that a local rejection mechanism against allogeneic tumor (Sarcoma 180), induced by injections of lentinan, failed to recognize autografts as “self” and destroyed them along with the allogeneic transplants.

The frequency of local tumor recurrence after surgical removal of the primary tumors and the development of new tumors in other parts of the mammary gland suggest that the rejection of autografts might be a strictly local process and that it does not induce adequate systemic resistance against the mammary tumor.

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