Reductive Effect of Aspirin Treatment on Primary Tumor Growth and Metastasis of Implanted Fibrosarcoma in Rats2

Abstract

For suppression of primary tumor growth and metastatic spread, aspirin and theophylline, either alone or combined, were given daily to inbred female BN rats after sc implantation of a syngeneic nonimmunogenic tumor. Treatment with 200 mg aspirin/kg (body wt) resulted in a statistically significant regression of tumor growth as well as of the number of metastases in the lungs. Aspirin given in a lower dose (20 mg/kg) did not show significant difference from the vehicle group. Theophylline (75 mg/kg) significantly increased primary tumor growth as well as lung metastases. Inhibition of in vitro platelet aggregation, determined in whole blood taken from non-tumor-bearing animals treated with the same therapeutic regimen, was most pronounced in those groups in which tumor growth and spread were significantly retarded. However, this positive correlation between inhibition of tumor spread and platelet aggregation was not associated with a favorable balance of prostacyclin and thromboxane A2 in these animals.