Comparative study of histopathologic characterization of azoxymethane-induced colon tumors in three inbred rat strains.

To obtain controlled genetic variation, colon cancer was chemically induced by use of four subcutaneous injections of azoxymethane (15 mg/kg of body weight/wk) to rats of 3 inbred strains (BDIX/OrlIco, F344/NHsd, WAG/Rij). The selection was based on the availability of established colon cancer cell lines arising from these particular strains. In the first experiment, only female rats were used; in the second experiment, both sexes were studied. The goal was to select a rat strain giving the highest tumor frequency with the shortest latency period in reproducible manner. The histologic characteristics should resemble the corresponding human tumors. The size of the tumors should be at about 1 cm in diameter, as these tumor cells were intended to be used in future transplantation studies. The two experiments yielded highly reproducible results: histologic evaluation of all colon tumors in all three rat strains revealed adenomas and adenocarcinomas closely resembling their human counterpart. The BDIX strain had the highest tumor frequency (75%) in both sexes and the shortest minimal latency period (28 weeks in experiment 1; 23 weeks in experiment 2). Tumor size of about 1 cm in diameter was found most often in the BDIX strain. On the basis of results of these two experiments, the BDIX strain has been selected for future study.