Objectives: To assess the effect of omega-3 fatty acids on:
Tumor incidence.
Clinical outcomes after cancer treatment.
Tumor behavior.

Data Sources: The researchers searched MEDLINE®, PreMEDLINE®, EMBASE, Cochrane Central Register of Controlled Trials, CAB HEALTH®, and contacted industry experts for unpublished data.

Review Methods: For tumor incidence, the studies were restricted to prospective cohort studies in humans, and for clinical outcomes after cancer treatment, studies were restricted to randomized controlled trials (RCTs). For tumor behavior, studies were restricted to review articles and meta-analyses of animal studies and cell culture studies in humans and animals. There were no language restrictions on any of the articles.

Results: Tumor incidence. Of 44 estimates of the association between tumor incidence and omega-3 fatty acid consumption, only 6 were statistically significant—2 each for breast cancer and lung cancer; 1 for prostate cancer; and 1 for skin cancer. Breast cancer and lung cancer each had a significant estimate for increased risk and another for decreased risk.
Cancer treatment. Relative to a standard enteral diet, omega-3 fatty acids in combination with arginine and RNA were associated with a statistically nonsignificant reduced risk of postoperative complications (RR = 0.51; 95% CI = 0.40, 0.64; P = 0.84) and a statistically significantly reduced length of hospital stay (pooled mean difference = -3.33 days; 95% CI = -4.29, -2.38; P = 0.001).
Tumor behavior. The researchers evaluated review articles on studies that described the effects of omega-3 fatty acids—animals or cell culture models—tumor growth, differentiation, or apoptosis. Much of the evidence favored a role for omega-3 dietary enrichment in the inhibition or prevention of tumor growth in some of the animal models.

Conclusions: In a large body of literature spanning many countries and cohorts with different demographic characteristics, the evidence does not suggest a significant association between omega-3 fatty acids and cancer incidence. In a small body of literature, there is no significant association between omega-3 fatty acids and clinical outcomes after tumor surgery. Although the combination of omega-3 fatty acids, arginine, and RNA are associated with a reduced risk of postoperative complications and reduced length of hospital stay, it is not possible to ascertain whether these effects are due to omega-3 fatty acids, arginine, RNA, or a combination of these. A large body of literature (of varying quality) suggests that omega-3 dietary enrichment may help inhibit or prevent tumor growth in some animal models; the quality of the review articles is not, however, sufficient to permit drawing strong conclusions.