PTGS2 and cancer: Among these, guanylate cyclase [52,53], metallothionein [54,55,56], homeobox [57], olfactory receptor [58], prostaglandin-endoperoxide synthase 2 [59], matrix metallopeptidase 12 [60], and chrysrallin [61] play roles in different types of pain, including visceral, neuropathic, and cancer-related pain.