Prevention and treatment of primary intestinal tumors in rats by piroxicam.

Over 90% of methylazoxymethanol acetate-treated male Lobund Sprague-Dawley rats developed intestinal tumors within 20 weeks; the incidence and numbers of tumors remained basically the same at 40 weeks. However, at week 40 the numbers of large tumors (greater than 0.5 cm in diameter) were increased. At week 40, tumors in methylazoxymethanol acetate-inoculated rats that had been treated with piroxicam (approximately 2.3 mg/day) from week 1 or from week 20 (after tumors had developed) were significantly reduced in numbers, but many large tumors persisted. Rats treated with piroxicam up to 40 weeks carried 0.6 tumor/rat compared with 2.7 tumors/rat among untreated controls (P less than 0.0001). Rats at week 20 had developed 2.8 tumors/rat and rats treated with piroxicam from week 20 to week 40 carried 1.4 tumors/rat (P less than 0.007). Most of the tumors in the piroxicam-treated rats showed evidence of histological differentiation.