Tumoricidal action of PUFAs on colorectal LoVo and RKO cancer cells in vitro was associated with increased formation of LXA4, decreased synthesis of PGE2 and LTB4 and suppressed expression of COX-2, ALOX5, mPGES, whereas 5-FU produced contrasting actions on these indices. This evidence concerns the gene PTGS2 and cancer.