Carcinogenicity of Long-Term Feeding of Cycad Husk to Rats∗

Summary Guamanians eat the fleshy husk of the seeds of the cycad, Cycas circinalis, which is indigenous to Guam. The fresh husk is eaten to relieve thirst. The dried husk is eaten as candy. The kernel of this seed is soaked in water, sun dried, and ground for preparation as an ingredient in foods. This processed kernel was not toxic or carcinogenic in contrast to unprocessed kernels. Since the husk is consumed without cooking or processing other than drying, and since the husk is reported to be eaten primarily by children, it is imperative to evaluate the safety of this food. The acute toxic effects have already been studied whereas the carcinogenic properties of the husk have not. For this reason rats were fed diets containing 0.5-2.0% of the dry husk for prolonged periods. Malignant tumors were found in the liver and kidney of experimental animals. Metastatic tumors were found in the pancreas, spleen, and lung.