Fish oil is a uniquely rich source of the long-chain omega-3 fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). A small structural difference distinguishes these fatty acids from the omega-6 fatty acids found in plant derived oils.
EPA and DHA have a valuable role to play in cancer treatment. A number of studies show that a diet rich in fish oil tends to slow tumor growth. At least part of this effect can be attributed to a suppressive effect of fish oil on angiogenesis. Remember, angiogenesis is the process by which new blood vessels develop to enable the growth and spread of tumors. EPA has been shown to decrease the expression of a key receptor in endothelial cells that makes them responsive to VEGF. Another key factor in angiogenesis is the enzyme Cox-2.
In endothelial cells, it produces prostanoids required for vascular tube formation during the angiogenic process. A high intake of fish oil has the potential to antagonize the role of Cox-2 in the angiogenic process by decreasing the production of Cox-2-derived prostanoids. It also may blunt the production of growth-promoting prostanoids in cancer cells.
Fish oil has the ability to fend off cachexia, the severe loss of muscle mass that often complicates late-stage cancer. Although cachexia usually entails a loss of appetite that can contribute to weight loss by decreasing calorie intake, the life threatening selective loss of muscle mass often seen in cancer patients reflects a very specific inflammatory process in muscle fibers that is not seen in healthy dieters. It has been discovered that EPA interferes with the inflammatory mechanisms that cause loss of muscle mass.