The present invention relates to the use of an oil enriched in docosahexaenoic acid, which is conjugated to triglyceride, for manufacturing a pharmaceutical composition for the treatment of a tumorous disease, said oil being enriched in a concentration of up to 70% by weight in relation to the total weight of said pharmaceutical composition, and said docosahexaenoic acid being in a percentage of at least 50% in relation to the total fatty acids in said oil.