PNPO and neoplasm: PNPO (EC 1.4.3.5) is an oxidase that plays a crucial role in the metabolism of vitamin B6 and acts as a cofactor for over 140 enzymes,[18, 19] which is widely distributed in various tissues.[20] However, excessive expression of PNPO is associated with tumor progression,[21] leading to increased proliferation and metastasis of cancer cells, such as in breast cancer[22] and ovarian cancer.[23] Despite this, more research is needed on the role of PNPO in MM.