A review of the current status of research on n-3 polyunsaturated fatty acids, eicosapentaenoic and docosahexaenoic, indicates that these fatty acids exhibit protective effects on: (i) the development of carcinogen-induced tumors, the growth of solid tumors, cachexia, and metastatic diseases in experimental models; and (ii) accelerated proliferation of flat human rectal mucosal epithelial cells in individuals at risk for colon cancer, and two biomarkers of risk for breast cancer--leukocyte adenosine diphosphate ribosyl transferase activity and 16-alphahydroxylated estrogen--in women at risk for breast cancer. These research findings, along with epidemiological evidence of an inverse relationship between n-3 fatty acid intake and incidence of some cancers, warrant clinical investigation in the potential benefit of n-3 fatty acids in the prevention and therapy of cachexia in cancer patients.