Treatment of chemically induced autochthonous rat mammary and colorectal carcinomas with interleukin-2.

The antineoplastic efficacy of human interleukin-2 (IL-2) in autochthonous methylnitrosourea-induced mammary carcinoma and in acetoxymethyl-methyl-nitrosamine-induced colorectal carcinoma of Sprague Dawley rats has been investigated. Under the conditions applied, IL-2 was non-toxic. In the mammary carcinoma IL-2 was therapeutically inactive. In the colorectal carcinoma, 1200 U IL-2/day exhibited significant antitumour activity in established tumours as well as in tumours treated "prophylactically" before their manifestation (P less than 0.05). The effect of IL-2 seemed to be more pronounced when given before manifestation of colorectal tumours (T/C = 8.7% vs 17.8% in established tumours). The differential sensitivity of the autochthonous mammary and colorectal carcinoma may be explained by differences in their proliferation rates and differences in volumes at the beginning of IL-2 therapy. IL-2 seems to be preferentially active in small tumours with a low proliferation rate, a feature typical of colon tumours.