A study on carcinogenesis induced by degraded carrageenan arising from squamous metaplasia of the rat colorectum.

We have undertaken studies on carcinogenesis arising from precancerous lesions, such as squamous metaplasia and ulcerative lesions of the rat colorectum, after termination of degraded carrageenan administration. Rates of tumor incidence in groups that were given a 10% diet of degraded carrageenan for 2, 6 and 9 months were 5 rats out of 39 (12.8%), 8 out of 42 (19.0%) and 17 out of 42 (40.5%), respectively. The colorectal squamous metaplasia persisted in all rats and progressed irreversibly. Degraded carrageenan was deposited not only in the colorectal propria mucosa, but also in the other reticuloendothelial organs. These results show that, even with short-term degraded carrageenan administration, degraded carrageenan is carcinogenic to the colorectum of the rat after a prolonged period.