The effect of daunomycin and adriamycin on the growth and regression of primary or transplantable murine sarcoma virus (Moloney)-induced tumors in mice has been studied. In the control groups, in most cases tumors regressed completely; tumor recurrence was observed in about 10% of the animals.

Treatment with daunomycin before infection inhibits the spontaneous tumor regression. Treatment with daunomycin after the infection causes a slight reduction of tumor size as compared to the controls and a high incidence of tumor recurrence. Recurring tumors progress until death of the animal. Tumor recurrence in daunomycin-treated animals depends on the age of the animal, daunomycin dose, and viral-infecting dose. Treatment with adriamycin before the infection causes delay and inhibition of tumor growth and does not affect tumor regression. Treatment with adriamycin after infection causes a greater reduction of tumor size than with daunomycin while tumor recurrence takes place later in time. In daunomycin- and adriamycin-treated animals, the titer of virus-neutralizing antibodies is equally reduced, and virus is present in the spleen.

The results show that both antibiotics have immunodepressive activity and suggest that adriamycin is less active than daunomycin in causing tumor recurrence or inhibiting tumor regression because of its higher effectiveness in destroying the primary tumor cells.

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Preliminary reports presented at the VIII Simposio Nazionale della Società Italiana di Cancerologia, Roma, December 1969, and at the Tenth International Cancer Congress, Abstracts, pp. 391–392, 1970, Houston, Texas, May 1970.

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