Former President Jimmy Carter’s announcement earlier this week that he is free of the melanoma that had spread to his liver and brain may be the highest-profile example yet of the promise of a new form of cancer treatment that unleashes an immune system attack on the disease.
Carter, 91, was treated with radiation therapy and the drug pembrolizumab (Keytruda), which releases a biological “brake” that can prevent the immune system from besieging and destroying tumor cells. Although doctors cannot be certain that the treatment is responsible for the remission of the disease, the improvement in Carter’s condition since beginning therapy is heartening physicians and patients around the world.
Radiation therapy and pembrolizumab are intended to work in tandem to defeat cancer, says Elizabeth Buchbinder, MD, a melanoma specialist at Dana-Farber. Radiation damages cancer cells and produces debris that attracts specialized immune system cells to the site of the damage. Pembrolizumab, a type of drug known as an immune checkpoint inhibitor, blocks a protein called PD-1 on the immune system cells that normally restrains them from attacking tumor cells. With PD-1 blocked the immune system can launch an all-out assault on the cancer.
The effectiveness of checkpoint inhibitors in many patients is especially rewarding to scientists such as Dana-Farber’s Gordon Freeman, PhD, whose early research into the basic workings of the immune system exposed the PD-1 trick by which cancer cells stave off an attack from the immune system. That research led to the development and testing of drugs like pembrolizumab, that allow such an attack to proceed.
Checkpoint inhibitors achieved their earliest success in patients with melanoma — and results with the PD-1 drugs have been good enough to lead to FDA approval for melanoma, lung and kidney cancer. Such drugs are now being tested, with encouraging results, against a variety of different types of cancer such as lymphoma, glioblastoma (a form of brain cancer), bladder cancer, head and neck cancer, and some ovarian cancers.
Says Dana-Farber’s F. Stephen Hodi, Jr., MD, a melanoma expert who led some of the earliest clinical trials of checkpoint inhibitors against the disease, “Anti-PD-1 therapy has revolutionized the way we care for patients with melanoma. It has up to 40 percent chance of shrinking disease and stabilization of additional patients. This reveals that many patients are trying to make an immune response against their cancer, but some natural brakes to the immune system are activated which the cancer takes advantage of. By blocking PD-1, one of the brakes to the immune system, the patient’s own immunity gets kicked into action to treat the disease.”
Learn more about the science behind immunotherapy in the video below: