COX-1 is a constitutive enzyme present in most human cells, either under physiological conditions or under disease conditions, while COX-2 is inducible and, therefore normally absent in human cells, but synthesized in large quantities within just a few hours of the onset of diseases involving the inflammatory process; large quantities of COX-2 are produced in chronic inflammation and cancer [145,146,147,148,149,150,151,152,153,154,155,156,157]. Here, PTGS2 is linked to cancer.