PTGS2 and colorectal carcinoma: It may also suggest an inductive effect of the tumour microenvironment on the adjacent non-tumour mucosa [24] Lin et al [7] in their study found a higher and more intense COX-2 expression by normal colon tissue compared to CRC tissues and hypothesized that the COX-2 expression by normal colonic mucosa adjacent to the tumour tissues modifies the tumour-stromal microenvironment thereby promoting tumourigenesis.