However, increased levels of COX-1 expression have been occasionally reported in several cancers [44], and it has been shown that the genetic disruption of COX-1 is as effective as COX-2 disruption in reducing intestinal [45] and skin tumorigenesis [46] in mouse models, thus suggesting that both COX isoforms could cooperate in the cancerogenesis process. This evidence concerns the gene PTGS1 and cancer.