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 (>0.5 cm in diameter) were increased. At week 40, tumors in methylazoxymethanol acetate-inoculated rats that had been treated with piroxicam (∼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 < 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 < 0.007). Most of the tumors in the piroxicam-treated rats showed evidence of histological differentiation.