For decades, studying the tumor microenvironment (TME) meant cataloguing its contents. But a new generation of technology is moving beyond characterization and toward predicting how tumors will behave and who will respond to treatment. The TME is more than a backdrop for cancer growth. It is a dynamic, densely populated ecosystem in which immune cells, stromal cells, blood vessels, and even microorganisms collectively determine whether a tumor thrives, spreads, or yields to therapy.