PTGS2 and cancer: The question can be raised to what extent the observed effect on death risk from cancer following use of either nonselective NSAIDs or COXIBs might be a consequence of primary chemoprevention because of an antimutagenic effect of COX-2 inhibition (i.e. inhibition of the appearance of the first malignant cells that later can give rise to a tumour cell population), and to what extent the death risk reduction might instead be explained as a consequence of delayed progression of the disease after it has started.