Effects of dietary omega-3 fatty acids on human breast cancer growth and metastases in nude mice.

BACKGROUND: Diets rich in omega-6 polyunsaturated fatty acids stimulate the growth and metastases of transplantable mammary carcinomas in rodents, whereas fish oil-containing diets, rich in omega-3 fatty acids, suppress the growth of these mammary tumor cells.
PURPOSE: This study was performed to evaluate the effect of a diet rich in menhaden fish oil on the growth and metastases of MDA-MB-435 human breast cancer cells in a mouse model system.
METHODS: Ninety female athymic nude mice (Ncr-nu/nu) were fed a 23% (wt/wt) corn oil, omega-6 fatty acid-rich diet; after 7 days, 1 x 10(6) estrogen-independent MDA-MB-435 human breast cancer cells were injected into a thoracic mammary fat pad. The 23% corn oil diet was continued for a further 7 days, after which the mice were assigned randomly to one of three diets containing a total of 23% fat, but different proportions of corn oil and menhaden oil (diet Cm: 18% corn oil and 5% menhaden oil, diet CM: 11.5% corn oil and 11.5% menhaden oil, and diet cM: 5% corn oil and 18% menhaden oil). Animal body weights and the surface area of the mammary fat pad tumors were recorded weekly. The mice were killed after 12 weeks on the experimental diets. Primary tumor surface areas and body weights were compared by unpaired Student's t tests, the incidence of lung metastases by the chi-square test, and differences in the total volumes of lung metastases by the nonparametric Mann-Whitney U test.
RESULTS: Tumor growth rates in the mice of the group fed diet Cm were significantly greater than for mice of either of the two groups fed diets containing higher levels of menhaden oil. Of the mice with primary tumors, the incidence of macroscopic lung metastases was greater in those fed diet Cm, compared with those fed diet cM (57.7% versus 22.2%; P < .01), but not significantly different from the mice fed diet CM. When metastases did occur, their extent was significantly greater in mice fed diet Cm, compared with those fed diet cM (P < .001).
CONCLUSION: These results indicate that a high-fat diet rich in omega-3 fatty acids can suppress human breast cancer cell growth and metastases in this mouse model system. IMPLICATION: Dietary intervention trials to reduce recurrence risk in the postsurgical breast cancer patient should take account not only of the level of fat consumed, but also its fatty acid composition.