Fish oil is often used to prevent heart disease but it has not been used for the treatment of cancer. Fish oil was recently studied because doctors believed that fish oil had the potential to cause cancer.
One article (1) discussed fish oil and its ability to cause cancer. It quoted a study from the Fred Hutchinson Cancer Research Center in Seattle, which indicated that fish oil might cause certain types of cancer.
It noted that many researchers feel that the study was flawed and didn’t accurately reflect the ability of fish oil to cause cancer. For this reason, unless further research is done on the risk of cancer using fish oil, it is perfectly safe to take fish oil in the prevention of prostate cancer.
Source: 1.Does fish oil cause cancer? http://www.drweil.com/health-wellness/health-centers/men/does-fish-oil-cause-prostate-cancer/. Accessed 8/27/16.