PTGS2 and neoplasm: There is some evidence that, besides the expression in tumour cells, COX-2 is also expressed in stromal cellular elements such as endothelial cells, macrophages, and fibroblasts (Masferrer et al, 2000), stimulated T-lymphocytes and activated mast cells (Iniguez et al, 1999; Hundley et al, 2001).