In the long struggle to understand why the immune system so often fails to defeat cancer from within, researchers have built a miniature replica of the tumor's hostile interior — a chip-sized window into the cellular betrayals that undermine immunotherapy. Working at a Chinese research institution, scientists discovered that macrophages and natural killer cells, two guardians meant to destroy tumors, instead trap each other in a self-reinforcing cycle of dysfunction, each making the other less capable of fighting. By mapping this hidden loop and testing drugs against it, the team not only expl