Jimmy Carter says he is cancer free and that recent tests do not show any signs of melanoma on his brain.

For now, Carter says he'll continue his regimen of immunotherapy, a treatment method that could offer a promising alternative to chemotherapy.

Chemotherapy can be hard on patients--along with killing cancer cells, it can also kill healthy cells. However, immunotherapy, which Carter has been receiving since August, is different.

Dr. Len Lichtenfeld of the American Cancer Society says that's because the drugs keep a patient's immune system from shutting down.

"The result is that the immune cells, once awakened, are able to attack the cancer cell and either destroy it, or, as in the case for some patients, basically keep it in check," he says.

He also says immunotherapy drugs may work to fight a number of different cancers.

"Not only melanoma, not only kidney cancer, but also head and neck cancer, breast cancer, there are reports even of ovarian cancer--a lot of cancers where we would not have expected these drugs to work," he says.

However, Lichtenfeld cautions that Carter hasn't just received immunotherapy. The former President's treatment regimen has also included surgery and radiation.

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