Difference Between Immunotherapy, Targeted Therapy and Chemotherapy

Aiwu Ruth He, MD, PhD, discusses the difference between chemotherapy, targeted therapy, and immunotherapy.

Chemotherapy is the traditional method used to treat cancer. Chemotherapy has been around the longest of the three treatment types and is generally aimed at rapidly growing cells. Unfortunately, aside from cancers, many of our own cells grow rapidly, such as blood cells, gut cells, and hair follicles, explaining some of the side effects of chemotherapy, e.g., fatigue, nausea and diarrhea, and hair loss.

Targeted therapy became a reality in the late 1990s and refers to treatments targeting known gene/protein alterations and cancer cell-signaling pathways. Side effects are specific to the pathway that is being targeted and are not the same as chemotherapy.

Finally, immunotherapy is the most recent treatment type, emerging over the last five years or so. Immunotherapy is best understood by considering how cancers develop. The cancer cells trick the immune system into believing that they should not be killed. Currently of most relevance, the immune system can be tricked into putting on its cancer-killing brakes. Checkpoint inhibitors (anti-PD-1 and anti-PD-L1) are a type of immunotherapy that removes these brakes and allows the destruction of cancer cells. However, if the patient’s immune system has not been tricked in this way, checkpoint inhibitors will not work. Research is ongoing to discover more ways cancer cells trick the immune system so that more immune therapies can be developed. Regarding side effects, releasing the immune-system brakes can increase immunity and cause immune-mediated side effects. This effect is not widespread across the body but can commonly involve the skin (skin rash), bowel (diarrhea), and lungs (cough, shortness of breath). The toxicity can often be treated with immunosuppressants such as corticosteroids, e.g., prednisone.