The anti-carcinogenic actions of omega-3 fatty acids derived from fish and fish oil may help reduce the risk of cancer development. Substantial evidence from animal and in vitro studies is leading to a swell of human studies attempting to unravel and explore the mechanisms by which omega-3 inhibits carcinogenesis. The headline “Taking omega-3 fish oil supplements may increase the risk of aggressive prostate cancer by 70%” was shouted in the Daily Mail in 2013 and whilst it didn’t take long for experts to expose the huge flaws within the study from which this alarmist message was plucked, many consumers, practitioners and health providers were considerably affected by this message, with many left questioning the safety of fish oils. The study from which this tabloid title was derived suggested that omega-3 fatty acid intake may be bad for prostate health, when the researchers had, in fact, reported that plasma phospholipid levels of total long-chain omega-3s, measured in blood samples collected at baseline, correlated positively with subsequent risk of both low-grade and high-grade prostate cancer in the SELECT trial, a study which never sought to investigate omega-3 levels.  By suggesting that intake of omega-3 plays a causative role in prostate cancer, the media managed to raise fears about fish and fish oil consumption that may have led to an adverse effect on public health, with over 12 million fish oil users reported to have stopped taking their omega-3.
Determining omega-3 levels in prostate tissue is a more accurate predictor than RBC levels for determine cancer risk
Omega-3 fatty acid intake from diet can be estimated with red blood cell (RBC) membranes or plasma. RBC omega-3 levels are generally accepted to be more accurate than plasma levels as they are correlated with long-term dietary intake. The levels within the tumour site itself, however, reflect the true degree of cancer progression: a recent study assessing omega-3 levels and prostate cancer progression found that whilst there was no significant difference between RBC membrane omega-3 fatty acids between individuals with non-progressive and progressive cancers, there were significant differences in the fatty acid profile within the prostate tissue itself. Patients with the lowest-progressive form of prostate cancer had the highest levels of omega-3 fatty acids at the tumour site and vice versa. When looking at the relationship of the two individual omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), EPA was the only fatty acid to be associated with reduced prostate cancer progression, suggesting that EPA rather than DHA may offer protection against prostate cancer progression.  The mechanisms by which omega-3 are linked to regression of tumours is complex and is thought to involve numerous genes that aid in the regulation of cell division and apoptosis (death) of cancer cells as well as inflammatory pathways. [3, 4] Elevated expression of pro-inflammatory markers is associated with poor prognosis, thus regulating inflammation is a key influencer in prostate cancer progression. The ratio of arachidonic acid (AA) to EPA (key omega-6 and omega-3 fats) in red blood cells is a recognised biomarker of inflammatory status and a high AA to EPA ratio is known to drive the inflammatory processes that are linked to cancer initiation and progression. 
Life-long EPA intake is most effective for reducing cancer risk
Higher intake of omega-3, both dietary and supplementary, is associated with a decreased risk of total and cancer-specific mortality.  Although most of the potential mechanisms by which long-chain omega−3 fatty acids may inhibit carcinogenesis are at the promotion and progression stages, the critical period for dietary exposure may be during childhood or early adulthood. This not only highlights the importance of EPA supplements throughout all life stages but also suggests that adopting an anti-inflammatory diet in early life may be particularly beneficial for optimal prostate health.
- Brasky TM, Darke AK, Song X, Tangen CM, Goodman PJ, Thompson IM, Meyskens FL, Jr., Goodman GE, Minasian LM, Parnes HL, et al: Plasma phospholipid fatty acids and prostate cancer risk in the SELECT trial. Journal of the National Cancer Institute 2013, 105:1132-1141.
- Moreel XX, Allaire J, Leger C, Caron A, Labonte ME, Lamarche B, Julien P, Desmeules P, Tetu B, Fradet V: Prostatic and dietary omega-3 fatty acids and prostate cancer progression during active surveillance. Cancer prevention research 2014.
- Larsson SC, Kumlin M, Ingelman-Sundberg M, Wolk A: Dietary long-chain n-3 fatty acids for the prevention of cancer: a review of potential mechanisms. The American Journal of Clinical Nutrition 2004, 79:935-945.
- Eser PO, Vanden Heuvel JP, Araujo J, Thompson JT: Marine- and plant-derived omega-3 fatty acids differentially regulate prostate cancer cell proliferation. Molecular and clinical oncology 2013, 1:444-452.
- Garassino M et al. A new biomarker in cancer patients: The arachidonic acid/eicosapentaenoic acid (AA/EPA) ratio First AACR International Conference on Molecular Diagnostics in Cancer Therapeutic Development, Sep 12-15, 2006