From what is known about effects of prostaglandins in cancer, as well as about COX-2 itself (since COX-2 is an enzyme that can also oxidize other substrates than polyunsaturated fatty acids, and some of the products of such reactions could be mutagenic), it must be judged most reasonable to believe that the main effect could be on the rate of progression of the disease (because of poorer angiogenesis, higher tendency for apoptosis among the tumour cells and better antitumour immunity) rather than an antimutagenic effect leading to primary chemoprevention. This evidence concerns the gene PTGS2 and cancer.