The role of diet and certain nutritional factors in the etiology or promotion of various malignant diseases has widely been studied. A link between dietary fat and cancer has long been proposed through various human epidemiologic and experimental data. High fat diets are associated with a high incidence and accelerated development of certain tumors, while there is evidence that dietary w-3 fatty acids have beneficial effects in cancer growth and metastasis. The relation between the different lipid formulations and cancer appears to be mainly related to the influence of specific fatty acids on the synthesis of the immunosuppressive prostaglandin E2. Omega-3 polyunsaturated fatty acids seem to have an anti-tumor effect through their immunomodulating, anti-inflammatory action and direct inhibition of tumor cell proliferation via alteration in prostaglandin E2 production.