Shh inhibitors also exert an anti-proliferative function by elevating 15-hydroxyprostaglandin dehydrogenase (15-PGDH), a prostaglandin E2 (PGE2)-degrading and tumour-suppressive enzyme [88], which subsequently inhibits cyclooxygenase-2 (COX-2) (Fig. 3). Here, HPGD is linked to neoplasm.