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Dietary Seaweed (Laminaria) and Mammary Carcinogenesis in Rats¹

Interdisciplinary Programs in Health, Harvard School of Public Health [J. T.]; Department of Pathology, Harvard Medical School [M. L. H.]; and Division of Biostatistics, Dana Farber Cancer Institute [R. S. G.], Boston, Massachusetts 02115

To test the potential in vivo antitumor effect of dietary seaweed, we induced mammary tumors in female Sprague-Dawley rats with the carcinogen 7,12-dimethylbenz(a)anthracene. Twenty-one-day-old rats (n = 108) were divided into two groups. Controls were fed a standard semipurified diet, and experimental rats received the control diet with 5% Laminaria, a brown seaweed, replacing 5% alphacel. At 55 days of age, each rat received 5 mg 7,12-dimethylbenz(a)anthracene intragastrically. Rats were palpated for mammary tumors and weighed weekly for 26 weeks. Complete autopsies were then done on all rats. The seaweed diet did not alter weight gain or weights of body organs at autopsy. Experimental rats had a significant delay in the time to tumor (p = 0.007); median time until tumor was 19 weeks in experimental rats and 11 weeks in control animals. Among mammary adenocarcinoma tumor-bearing animals, experimental rats had fewer adenocarcinomas/individual (p < 0.05). There was also an overall 13% reduction in the number of experimental rats with histologically confirmed adenocarcinomas (76% among the control rats compared to 63% among the experimental rats). Components of Laminaria which might account for the observed difference in mammary tumor growth are varied and include the sulfated polysaccharide fucoidan. Rats in the top row of cages had a significant (p = 0.01) delay in time to tumor compared to rats in the lower four rows. In each row, the seaweed-fed rats had a longer time to tumor than did the control rats.

¹ This investigation was supported by the Wallace Genetic Foundation, Andrew Mellon Foundation, the Exxon Education Foundation, USPHS Grant 5T32 RR07000 in veterinary and comparative pathology, and National Cancer Institute Cancer Center Support Grant CA06516. Presented in part at the International Association for Breast Cancer Research, Denver, CO, 1983 (22).

² To whom requests for reprints should be addressed, at the Division of Biostatistics, Dana Farber Cancer Institute, 44 Binney Street, Boston, MA 02115.

Received 7/ 5/83. Accepted 4/11/84.

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