Alteration of tumor growth by aspirin and indomethacin: studies with two transplantable tumors in mouse.

Oral daily administration of aspirin or indomethacin retarded growth of experimental tumors in mouse. Aspirin treatment, 150 mg/kg twice daily, inhibited growth of a transplantable mast-cell ascites tumor (P815) by 39-43% (p less than 0.001) and of a s.c. transplanted Lewis lung carcinoma by 52% (p less than 0.025) without adversely affecting body growth. The total serotonin, histamine and histidine decarboxylase content of the ascites tumor was also reduced as was the urinary excretion of the amines. Treatment with 3 and 5 mg/kg indomethacin resulted in 40% (p less than 0.01) and 80% (p less than 0.001) reduction, respectively, in ascites tumor growth. With the higher dose of indomethacin, no tumor was observed in half of the animals inoculated with tumor, although signs of indomethacin toxicity (reduced body growth, gastric lesion) was evident in the animals.