SELENOP (selenoprotein P) is a hepatically-synthesized selenoprotein that functions as the primary selenium transport molecule in circulation 1. As a selenium carrier, SELENOP delivers selenocysteine to peripheral tissues including brain and testis, enabling the synthesis of essential selenoproteins like GPX4 that prevent ferroptosis 2. SELENOP exhibits extracellular antioxidant defense properties and participates in cellular responses to oxidative stress through selenium binding 3. Beyond selenium transport, SELENOP modulates WNT signaling by interacting with the coreceptors LRP5/6, promoting canonical WNT pathway activation 4. In cancer immunology, SELENOP-expressing macrophages represent a novel immune cell subset with critical roles in tumor microenvironment remodeling. These cells accumulate in tertiary lymphoid structures and cooperate with antigen-presenting fibroblasts to recruit CD4+ and CD8+ T cells through cholesterol, interleukin, and chemokine pathways 5. SELENOP-macrophages are significantly enriched in responders to neoadjuvant chemoimmunotherapy and are abundant in lung adenocarcinoma, where they exhibit antitumor functions 6. Clinically, SELENOP represents a hepatokine influencing systemic metabolic health and neurodegeneration risk; hepatic copper accumulation impairs SELENOP secretion, potentially compromising selenium delivery to the brain 17. LRP8-mediated SELENOP uptake is essential for protecting MYCN-amplified neuroblastoma from ferroptosis, representing a tractable therapeutic vulnerability 2.