International Agency for Research on Cancer (IARC) - Summaries & Evaluations


VOL.: 1 (1972) (p. 157)

5. Summary of Data Reported and Evaluation

5.1 Animal carcinogenicity data

Cycasin is carcinogenic in five animal species, inducing tumours in various organs. Following oral exposure, it is carcinogenic in the rat, hamster, guinea-pig and fish. By this route, the data in the mouse is of borderline significance and the negative experiment in chickens only lasted 68 weeks. It is active in single-dose experiments and following prenatal exposure. The carcinogenicity of its metabolite, methylazoxymethanol, has been demonstrated in the rat and the hamster and that of a closely related synthetic substance, methylazoxymethanol acetate, in the rat.

5.2 Human carcinogenicity data

Nuts prepared in Guam in the usual way (leached with water and sun-dried) were reported still to contain 160 ppb of cycasin. In another report, chips of dried kernels of cycad nuts did not contain cycasin. The epidemiological study in the Miyako Islands involved a follow-up after heavy exposure in 1959 for the years 1961 to 1966, which may have been too short for a carcinogenic effect to be observed. However, there was also chronic exposure prior to 1959 in this population. It is noteworthy that an increased mortality from cirrhosis was observed. This negative result concerning cancer in the only epidemiological study performed to date is insufficient to exclude a possible carcinogenic effect of cycasin on man.

Subsequent evaluation: Vol. 10 (1976); Suppl. 7 (1987) (p. 61: Group 2B)

For definition of Groups, see Preamble Evaluation.

Last updated: 12 March 1998

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