Omega-3 fatty acids could be a safe and beneficial booster for tamoxifen therapy, according to researchers at Fox Chase Cancer Center in Philadelphia. The fats—abundant in fish—produced a greater expression of genes that indicate lower cancer severity than did corn oil in an animal model of breast cancer.

The study, led by Andrea Manni, MD, of Penn State University, involved four groups of rats in which mammary tumors had been induced. Two groups were fed a 17% fish-oil diet, with or without tamoxifen, and the other two received a 20% corn-oil diet, with or without tamoxifen.

After the 8-week diet ended, the researchers analyzed gene expression patterns in the tumors. Compared with corn oil, omega-3 fatty acids produced a greater expression of genes related to cellular differentiation, a sign of lower cancer severity.

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“If a tumor was being treated with tamoxifen, the addition of an omega-3 fatty acid diet seemed to make the tumor—at least at the molecular level—more benign and less aggressive and responsive to tamoxifen,” affirmed Jose Russo, MD, in a statement describing the results. Russo, director of the Breast Cancer Research Laboratory at Fox Chase and part of the study team, presented the results at the annual meeting of the American Association for Cancer Research (AACR), held April 2-6, 2011, in Orlando, Florida. 

In addition to reducing the expression of genes linked to tumor growth and metastasis, the combination of fish oil and tamoxifen was more effective than corn oil in increasing the expression of genes related to immune defenses against tumors. However, the omega-3 diet also increased gene expression related to inflammation, allergic reactions, and other counterproductive immune responses that limit the ability of cells to fight cancer and can even promote the migration of tumor cells.

As Russo noted, more studies are needed to fully understand the effects of fish oil on the immune system.