targeted therapy

A targeted therapy is a cancer drug aimed at a specific molecule that a particular tumor depends on, rather than at any cell that happens to be dividing. The idea is to find the broken switch or overactive engine that is driving a cancer, and shut down that exact part. Compared with old-style chemotherapy, which carpet-bombs all fast-dividing cells, targeted therapy is more like a precision strike.

These drugs work because many cancers are addicted to one or a few aberrant proteins — often a mutated, fused, or amplified enzyme that keeps growth signals switched on. Block that protein and the tumor's lifeline is cut. Targeted agents come in many forms: small molecules that fit into a binding pocket, antibodies that latch onto a surface receptor, and newer designs that drag a target off for destruction.

Because the effect depends on the tumor carrying the right molecular driver, targeted therapy usually goes hand in hand with a diagnostic test to pick patients whose cancer has that feature. Its great weakness is resistance: tumors evolve, and a single new mutation in the target can render a once-effective drug useless, which is why later-generation drugs and combinations are constantly developed.