The 6th most common form of cancer in the world, liver cancer has gained attention recently for being responsible for taking David Bowie’s life. While surgery is currently the only effective treatment recognized by conventional medicine, new research has revealed exciting new ways to wipe out liver cancer cells without harming healthy cells – a fish oil component known as DHA (docosahexaenoic acid), encapsulated in the low-density lipoproteins (LDL) infamous for cholesterol transportation. 
“This approach offers a potentially new and safe way of treating liver cancer, and possibly other cancers. The method utilizes the cholesterol carrier LDL, combined with fish oil to produce a unique nanoparticle that is selectively toxic to cancer cells,” said study senior author Dr. Ian Corbin, Assistant Professor in the Advanced Imaging Research Center (AIRC) and of Internal Medicine at UT Southwestern. “
Using a fatty acid commonly found in fish oil may seem unusual, but this research was inspired by the number of studies showing a preventative effect of fish oil on cancer. For example, a 2012 study in Gastroenterology revealed that fish oil consumption helped to prevent development of liver cancer in patients with hepatitis B and C infections. However, there has been no research on the ability of omega-3 fatty acids to treat already-established tumors, which would require a more targeted approach than diet.
As cancer cells take up large amounts of LDL in order to acquire fats and cholesterol to help build their cell membranes, scientists decided to “trick” them by replacing the cancer-safe fats inside the LDL particles with DHA. These LDL-DHA particles were then injected into rats with liver cancer, specifically into the artery leading to the liver. Control rats were injected with “regular” LDL particles.
The control rats exhibited tumor growth over the next three days and had a sufficient blood supply. The treated rats had smaller, paler tumors with poor blood supply, and over 80% of the tumor cells were dying.
These results were very impressive, but more research is needed to confirm these effects in other cancer types and in humans.
For more than just Liver Cancer
Intake of eicosapentaenoic acid (EPA) and DHA, both omega-3 fatty acids found in fish oil, reduce the risk of more than just viral liver cancer. A 7-year study on over 3,000 women who previously had early-stage breast cancer showed that women with higher EPA and DHA intakes had an approximately 26% reduced risk of recurrence in the second tertile of consumption, and a 28% reduced risk in the highest tertile. Women in the second tertile also had a 25% reduced risk of all-cause mortality; this was a 41% reduced risk in the highest tertile.
These effects were found to be caused by dietary intake, not supplementation, which may imply oxidation of the supplemental oil or a synergistic effect between the oil and other nutrients in fish.
In another study, this time on prostate cancer, fish consumption had “no effect” on the incidence of prostate cancer, but instead reduced the risk of dying from the disease by 63%. To break the results down, the cohort studies showed no effect, but the case-control studies showed a 15% lowered risk.
There was only one study found on risk of metastatic disease, in which fish consumption was linked with a 44% risk reduction, with a “confidence interval” of a 14-63% reduced risk. A large study of 46,465 Japanese men showed a 39% reduced mortality risk for eating fresh fish, but was not included because it differentiated between fresh and preserved fish instead of just giving a relative risk for fish in general.
Data from the SELECT study (Selenium and Vitamin E Cancer Prevention Trial; closed in 2014) shows that EPA and DHA raise prostate cancer risk, but that conclusion was based on blood levels of these fatty acids. The blood levels reflected recent intake and most likely that the men started taking them after diagnosis. The study also had other flaws, such as using synthetic, rather than natural vitamin E.
Some evidence that fish oil may not work best alone comes from a laboratory study which found that fish oil increased the anticancer effects of vitamin D3, besides having anticancer effects on its own. With the protective effects of omega-3 fats against cancer, it makes sense to change the fatty acid composition of one’s diet to the optimum ratio, seen as anywhere from 5:1 to a 1:1 of omega-6 to omega-3 fats, as prevention is far better than needing treatment.