In the long struggle to understand why lung cancer so often evades the body's defenses, researchers at Columbia University have found a hidden collaborator: a previously uncharacterized cell that actively recruits the immune system's own peacekeepers to stand guard around tumors. Published in Nature Immunology, the discovery identifies fibroblasts marked by the gene CHL1 — cells absent in healthy lungs but abundant in cancerous ones — as architects of a zone of immune tolerance that allows tumors to grow unchecked. The finding matters not only as a map of cancer's cunning, but as a potential o