The invention relates to a composition comprising a combination of the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The composition can be used for enhancing the activity of chemotherapy or radiotherapy and/or in the prevention or reduction of side effects caused by the chemotherapy or radiotherapy in a patient ill with cancer, the composition being intended for administration to the patient prior to the commencement of a cycle of chemotherapy or radiotherapy.
