Carcinogenic Properties of Nuts From Cycas Circinalis L. Indigenous to Guam

Summary

Neoplastic disease in rats developed after chronic ingestion of cycad nut meal as a part of the diet. The nuts, obtained from the plant Cycas circinalis L. indigenous to Guam, originally were suspected of possessing a neurotoxin. Although the experiments failed to demonstrate this effect, benign and malignant tumors developed, mainly in the liver and kidneys, with 1 in the lung and 2 in the intestine. The tumors in the liver were hepatocellular carcinomas and reticuloendothelial neoplasms, occurring simultaneously but independently. The tumors in the kidney were adenomas and undifferentiated tumors, bilateral and simultaneous. The tubular adenomas grew expansively. The undifferentiated tumors were thought to have originated from cells between tubules and capillaries in the inner cortex and grew infiltratively between pre-existing renal structures. Peculiar vascular changes characterized by subintimal hyalinosis of capillaries and limited to the undifferentiated tumors were described and thought to represent a secondary phenomenon. The similarities in pathologic changes between rats fed toxic cycad nut meal and those, reported in the literature, given dimethylnitrosamine were emphasized, and the possibility was suggested that a glycoside isolated from cycads, namely cycasin, may yield in its metabolic breakdown a compound carcinogenic for rats and similar to the one suggested as the carcinogenic agent in dimethylnitrosamine. This possibility is currently being investigated.