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Health See other Health Articles Title: Marine Oils Lower Risk for Colorectal Cancer Subtype Medscape... Fish oil intake does not appear to have a protective effect against the development of colorectal cancer overall, although it was found to be associated with a lower risk for one particular subtype in newly reported research. Specifically, the study found that a high intake of marine omega-3 polyunsaturated fatty acids (PUFAs) was associated with a lower risk for microsatellite instable (MSI)–high colorectal cancers, but it did not affect the risk of developing microsatellite stable (MSS) tumors. The findings were published March 25 in the Journal of the National Cancer Institute. Only about 10% to 15% of colorectal tumors display MSI, which is caused by the loss of DNA mismatch repair activity, note the authors, led by Mingyang Song, PhD, from the Department of Nutrition at the Harvard School of Public Heath, in Boston, Massachusetts. Chronic inflammation is involved in the development of both colorectal cancer and MSI, and experimental research has shown that marine omega-PUFAs have potent anti-inflammatory activity and inhibit colorectal carcinogens. However, epidemiologic data on the association between marine omega-3 PUFAs and colorectal cancer have been inconsistent. Dr Song and colleagues investigated whether the association between marine omega-3 PUFAs and colorectal cancer differed by MSI-defined tumor subtypes. They used data drawn from the Nurses' Health Study and Health Professionals Follow-up Study. In these two large cohorts (121,701 registered female nurses and 51,529 US male professionals), the authors documented and classified 1125 cases of colorectal cancer into either MSI-high tumors (in which 30% or more of the 10 microsatellite markers demonstrated instability) or MSS tumors. They then examined the association of marine omega-3 PUFA intake with both overall and MSI-defined colorectal cancer in the two patient groups. Participants with higher intakes of marine omega-3 PUFA were more likely to be active, to be regularly taking multivitamins and fish oil supplements, to undergo lower gastrointestinal endoscopy, and to have more frequent consumption of poultry, fruits, and vegetables and less less consumption of unprocessed and processed red meat. Although they found that dietary intake of marine omega-3 PUFA was not associated with an overall incidence of colorectal cancer, there was a statistically significant difference when it was analyzed by MSI status (P heterogeneity = .02). A high intake was associated with a lower risk for MSI-high tumors (comparing ≥0.30g/day with <0.10g/day: multivariable HR = 0.54; P linearity = .03), but this association was not observed for MSS tumors (HR = 0.97; P linearity = .28). This association also appeared to be independent of CpG island methylator phenotype (CIMP) and BRAF mutation status. "Our findings generate hypotheses for the potential anticancer activity of omega-3 PUFAs and may have clinical implications for the potential of using marine omega-3 PUFAs in prevention of CRC," the authors conclude. "Fish-ful" Thinking? However, in an accompanying editorial, Asad Umar, DVM, PhD, Ellen Richmond, GNP-BC, and Barnett S. Kramer, MD, MPH, all from the National Cancer Institute, advise caution when interpreting these findings. They point out that the role of marine omega-3 in colorectal cancer prevention continues to be unclear and "remains elusive despite decades of effort." The results of the current study "add another layer of confusion to the endeavor," they comment. Potential sources of bias, such as measurement error and selective publication of positive results, must first be considered, the editorialists note. They point out that it is particularly difficult to accurately collect data on long-term intake of nutrients. "In addition, adipose tissue samples may reflect highly variable cumulative fatty acid content at a single time point, rather than fatty acid content over time," they write. Previous studies have shown findings similar to those reported in the current article, but there is still an absence of robust associations for marine omega-3 fatty acids and the overall risk of colorectal cancer, Dr Umar and colleagues say. Thus, these "puzzling results of the seemingly contradictory studies must be sorted out before fish diets for general colorectal cancer prevention can be recommended." "We cannot let premature fish-ful thinking lead to public health recommendations without further study," they write. We cannot let premature fish-ful thinking lead to public health recommendations without further study. Dr Asad Umar and colleagues The editorialists also point to the fact that two large prostate cancer prevention trials found omega-3 serum levels to be associated with an increased prostate cancer risk, and this leads one to speculate whether omega-3 PUFA levels or fish consumption may be surrogates of exposure to environmental carcinogens associated with marine-based foods in those situations. This work was supported by the National Institutes of Health and by a grant from the Agrusa Fund for Colorectal Cancer Research. Study author Andrew Chan, MD, previously served as a consultant for Bayer Healthcare, Millennium Pharmaceuticals, Pfizer Inc., and Pozen Inc. The editorialists have disclosed no relevant financial relationships. J Natl Cancer Inst. 2015;107:djv007. Full text, Editorial Editors' Recommendations Fish Oil May Guard Against Alcohol-Related Brain Damage High Levels of Fish Oil May Boost Risk for Prostate Cancer Specific Fish Oils May Protect Against Breast Cancer Post Comment Private Reply Ignore Thread
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