Immunotherapy
Any treatment that works by getting the patient's own immune system to attack the cancer, rather than attacking the cancer directly. It can produce responses that last for years, but only in some patients.
The main forms are checkpoint inhibitors (antibodies that release the brakes on T cells), cell therapies (CAR-T, TCR-T and TIL, in which a patient's T cells are removed, engineered or expanded, and returned), bispecific T-cell engagers, cancer vaccines including personalised mRNA vaccines, cytokines, and oncolytic viruses. Because the immune system has memory, responses can persist long after treatment stops, which is why the survival curves for melanoma and lung cancer now show a plateau of long-term survivors; the flip side is autoimmune side effects and the fact that many tumours remain 'cold' and unresponsive. Predicting who will respond, and turning cold tumours hot, are two of the field's central problems.