Former President Jimmy Carter, who turns 100 today, may have had a mixed legacy of political achievements, but in the field of cancer treatments, he helped put immunotherapy on the map.

Carter’s remarkable recovery in 2015 from advanced melanoma — previously a certain death sentence — made the public aware of the benefits of checkpoint inhibitors, drugs that help the body’s own immune system recognize and attack cancer cells, explains the American Cancer Society.

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Carter, the oldest living former commander in chief, also survived metastatic brain and liver cancer due to the spread of melanoma. He entered hospice care at home in Plains, Georgia in February 2023.

Just four months after Carter announced he had metastatic melanoma that had spread to his liver and brain, the nonagenarian said he was cancer-free following radiation therapy and treatment with cancer immunotherapy, says the American Association for Cancer Research.

He received the intravenous drug called pembrolizumab, or Keytruda, in 2015, at the age of 91 to treat the melanoma.  According to The Washington Post, the Merck medication blocks a checkpoint called PD-1 and is now used to treat many cancers after its approval in 2014.

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“My most recent MRI brain scan did not reveal any signs of the original cancer spots nor any new ones,” the former president said. “I will continue to receive three-week immunotherapy treatments of pembrolizumab.”

Carter’s recovery from a deadly cancer stunned both the public and the oncology world. It triggered what experts call “the Jimmy Carter effect” that had patients clamoring for the drug, saying “I want what Jimmy Carter had,” according to STAT News

“Holy smoke, this stuff actually works,” said Dr. Norman E. Sharpless, the former director of the National Cancer Institute. Today, checkpoint inhibitors, given as infusion into a vein, are approved for more than 20 malignancies, says the Post, including cancers of the kidney, head and neck, and some lung cancers. They are frequently used with other therapies such as other forms of chemotherapy and medication. About 39% of the nearly two million cancer cases diagnosed annually in the U.S. may be eligible for immune checkpoint inhibitor drugs, according to JAMA Network Open.

The annual cost of these intravenous medications is well over $100,000 but government and private health insurers typically cover the expense, with out-of-pocket costs varying according to individual health plans.

Experts warn that while immunotherapy has cured some cancer patients and extended the lives of others the response rates vary between 10% and 60% depending on the type of cancer and whether medications or therapies are used.

Some oncologists are focusing their research on why immunotherapy works in some patients, and against some tumors, but not others. The checkpoint inhibitors have had the most success in advanced melanomas, like in Carter’s case. Before these drugs, patients typically survived a matter of months. Now the five-year survival rate is around 50%, says the Post. But half the patients with later-stage melanoma do not respond to the medications.

Carter taught the public an important lesson about new treatments, says the Post, and the hope they can provide. In recent years, immune therapies have become the fourth pillar of cancer treatment, following surgery, radiation, and chemotherapy.  Along with checkpoint inhibitors, CAR T-cell therapy was approved in 2017 and is sometimes used for blood cancers such as leukemia and lymphoma.

Experts say that the checkpoint drugs are most effective in advanced melanoma, as witnessed in “the Jimmy Carter effect.” “It has been paradigm-changing,” said Dr. Cary Gross, of Yale School of Medicine.

Carter, a former Sunday school teacher, taught the public important lessons about new treatments and the hope they can provide, Gross said. Carter also shared his thoughts about the value of hospice by making public his decision about end-of-life care.