Endemic and Morphologic Similarities Existing between Spontaneous Colonic Neoplasms in Man and 3

Abstract

An endemic of adenomatous polyps and adenocarcinomas induced in 92 rats by the injection of 3:2[image]-dimethyl-4-aminobiphenyl in peanut oil is compared with the endemic of colonic neoplasms occurring spontaneously in Americans. Morphologically the adenomatous polyps and adenocarcinomas were similar in both rat and man. The neoplasms of rats were homogeneous on step sections and were sharply demarcated from adjacent normal mucosa. No morphologic evidence of transition from benign to malignant could be found. The tumors within the rat colon had a segmental distribution similar to that observed in human colons. The percentile distribution of cancers per unit length of colon was greater than that of adenomatous polyps in the rectum and cecum and the ratio was reversed in the intervening colon. Essentially, the male rats developed only colonic neoplasms but extracolonic neoplasms were very frequent in the female rats. In both the rat and human, endemic multiple neoplasms occur with great frequency if populations are observed to the terminus of life. In both rat and man, the prevalence of neoplasms increases sharply with the aging of the host populations. A list of polycyclic hydrocarbons reported to have induced intestinal neoplasms in small animals is reported. Several of these compounds have also induced urinary bladder tumors in both rat and man. In man, bladder tumors continue to appear with increasing prevalence 15 to 20 years after exposure to 4-aminobiphenyl. The very slow rates of growth of human colonic neoplasms would be associated with equally long periods between associated with equally long periods between exposure to a carcinogen and the appearance of a symptomatic neoplasm.