Immunotherapy may also be referred to as “checkpoint inhibitors” because these drugs override the immune system’s mechanisms of restraint to increase recognition and activation of an immune response against tumor cells. A great metaphor is that CTLA-4, PD-1, and PD-L1 inhibitors “take the brakes off,” allowing the immune system to “rev up” to fight cancer .
However, as anyone who has ever studied autoimmune disease knows, an overactive immune system can cause damage of its own. Immunotherapy can cause side effects that range from mild to life-threatening in virtually every organ and system; if side effects are severe that is an indication to halt treatment. The decisions on how to manage these toxicities (immune-related adverse effects) are complicated, and while there are guidelines on when/how to treat, the most important part is recognizing a toxicity in the first place–so keep an eye out.