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Hank: In August 2015, the 91-year-old former US President Jimmy Carter announced that he had a form of cancer that had spread to his liver and brain. The diagnosis is about as good as it sounds... which is to say, not good. But then, just a few months later, Carter reported that his cancer was gone, partially thanks to a pretty new treatment called immunotherapy. And in March, doctors determined that he didn’t need any treatment anymore. So how did he recover so quickly? And what does that recovery mean for the future of cancer treatments?

To understand what Carter’s treatment can teach us, you first have to know a little bit about cancer. Cells in your body normally grow and divide every so often to replace themselves. Cancer is what happens as a result of abnormal, uncontrolled cell division. Each type of cancer is caused by different kinds of genetic mutations, and cancerous cells can grow too much and spread to almost any kind of tissue in the body -- which is called metastasis.

Because of this, different types of cancer in different people may or may not respond to a particular treatment. In other words, what works for one patient might not help another, even if they have the same kind of cancer. So medical professionals usually combine treatments for cancers depending on the type, stage, location, and the patient’s health. For example, surgery aims to remove the cancerous tumors directly, while radiation uses high-energy particles to tear up the DNA of those mutant cells. Chemotherapy is a mixture of drugs added to a patient’s bloodstream to hopefully keep cancer cells from dividing.

But, recently, a newer method of treatment called immunotherapy has been getting attention, and it’s probably what saved Jimmy Carter’s life. Your immune system is your own personal bodyguard -- specialized organs, cells, and chemicals that protect your body from infection and disease. If everything’s working properly, your immune system should know you friend -- one of your own cells -- from your foes -- like a germ that shouldn’t be there. But cancer only spreads when the immune system can get... confused. The immune system can’t always recognize these mutated, multiplying cancer cells as foreign foes they’re basically hiding in plain sight.

Not only that, but some cancer cells can dampen your immune response, so even if the immune system is like, “Hey! Code Red! We’ve got cancer over here!” it can’t kill the dangerous cells without extra help. So, researchers have been working on ways to help the immune system recognize cancer cells and fight back, like by adding man-made proteins to give it a boost.

Immunotherapy isn’t exactly new -- it’s a range of strategies that doctors have used, along with other treatments, for a couple of decades already. But it’s gained a lot of momentum in the last few years. In September 2014, the US Food and Drug Administration granted accelerated approval to a new drug for patients in life-threatening stages of certain types of cancer, who had exhausted other treatment options -- including Carter, with his advanced melanoma.

See, certain healthy cells in our bodies express a protein called PD-L1, to activate the PD-1 cellular pathway and help suppress certain cells in the immune system. But melanoma cells can /also/ express PD-L1, which activates the same pathway and helps them essentially hide from immune cells. The drug pembrolizumab [pem-broh-LIH-zoo-mab], also known as Keytruda, was the first FDA-approved drug designed to block the PD-1 pathway, so the immune cells can recognize and get rid of those cancerous tumors. The initial melanoma treatments that involved Keytruda didn’t work any better for some patients, but others -- like Jimmy Carter -- watched their tumors significantly shrink, or even vanish, within months.

Now, despite a bunch of headlines that say that this is a “miracle cure,” it would be hasty -- and maybe even a little dangerous -- to say that Carter and other patients like him are just “cured.” Even if cancer is no longer detected on a scan, that doesn’t necessarily mean it’s gone, or it won’t return. Some of those mutated cells could still survive and start to multiply again. So Carter’s doctors will still periodically scan to check his brain and liver tissues, even though he’s currently stopped all treatments. That’s why people talk about being in remission, rather than being cured of cancer entirely.

Still, Keytruda’s results seem very promising. Researchers hope to keep developing and expanding this kind of immunotherapy treatment to other types of cancers. And studies on lymphoma, breast cancer, and bladder cancer are already up and running. So immunotherapy in my opinion, is now officially a promising weapon in the multi-treatment fight against cancers.

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