In vitro chemosensitivity tests on human tumor xenografts by clonogenic assay: the combined use of mitomycin C with alpha-interferon or gamma-interferon.

Using the human tumor clonogenic assay technique, the effects of Mitomycin C plus either alpha-interferon or gamma-interferon were studied against five human tumor xenografts serially transplanted into nude mice (three gastric and two colon cancers). When the survival fraction found with the drug combination was smaller than the multiplication of survival fractions with either drug alone, the combined effect was defined as synergism. Similarly, antagonistic effect was defined when the survival fraction of drug combination was larger than the larger one observed in either interferon or Mitomycin C alone. Four out of five human tumor xenografts (three gastric and one colon cancers) showed synergistic effects in combination of alpha-interferon with Mitomycin C. Though two gastric cancer xenografts exhibited synergistic effects in combination of gamma-interferon with Mitomycin C, antagonistic effects, which was not found in combination of alpha-interferon with Mitomycin C, were observed in one gastric cancer and one colon cancer xenografts.