HPGD and colorectal carcinoma: The gene expression of COX-1 (gene name PTGS1) and 15-PGDH (gene name HPGD), involved in the metabolism of PGE2 to the less active 15-keto-PGE2 (Tai et al., 2002) was significantly downregulated in CRC tissues vs. normal mucosa (Figure 5D).