It’s difficult to know exactly how much credit should be given to the immune system-based drug therapy former President Jimmy Carter received in his successful cancer treatment.

But one thing is for certain.

The high-profile case appears to be shining a brighter and more favorable spotlight on immunotherapy as a way to battle cancer.

Medical experts interviewed by Healthline were quick to point out that other factors such as surgery, radiation, and even the 91-year-old former president’s genetics could have played a major role in his recovery.

However, they all agreed that cancer treatments that bolster a patient’s immune system rather than flood them with chemicals appear to be the future.

“It leads me to be optimistic, although we still have a ways to go,” Dr. Len Lichtenfeld, the deputy chief medical officer for the American Cancer Society, told Healthline.

Read More: Immune Systems Now Major Focus of Cancer Treatment Research »

Carter’s Rapid Recovery

Carter announced over the weekend at a Sunday school class in his hometown of Plains, Georgia, that he no longer needs cancer treatment.

The former president began treatment in August after doctors discovered melanoma had spread from his liver to his brain.

At the time, there were experts who predicted Carter would live just a matter of months and the treatment was more for his quality of life than extending it.

However, in December, the former president said there was no longer any cancer in his brain, but that he would still continue his treatment with the immunotherapy drug Keytruda.

Those treatments are now being stopped. Litchenfeld noted Carter and his doctors haven’t said why.

It could be that they simply aren’t needed any longer, or the former president could be having side effects.

“The bottom line is we can only speculate why they decided to stop treatments,” Lichtenfeld said.

He added surgery was also done to remove the cancer from Carter’s liver and intense radiation treatment was done on the cancer spots in his brain.

It could have been a combination of factors that eradicated the cancer.

But Lichtenfeld said that the fact the cancer hasn’t returned is good news and an indication that the immunotherapy is at least partly responsible.

“All of that is very positive,” he said.

Read More: Safer, Quicker Breast Cancer Treatment Gets a Boost »

How Immunotherapy Works

Keytruda is one of several new drugs that battle cancer by simply bolstering a patient’s immune system.

Cancer cells are known to send out signals that disable the immune system or at least trick it into thinking the foreign invaders are not a threat.

The cells do this by emitting a protein that deactivates T cells, the immune system’s key defenders.

Keytruda and other new drugs block the activities of the protein, allowing the T cells and the immune system to go after the cancer growths.

Keytruda was approved by the Federal Drug Administration (FDA) in September 2014 for treatment in late stage melanoma. Last October, it was given the OK for use against advanced non-small cell lung cancer.

The drug Opdivo is also being used to treat late stage melanoma. It received FDA approval in December 2014.

Read More: Would Cal Quarterback Joe Roth Have Survived His Melanoma Today? »

The Advantages of Immunotherapy

Medical experts say there are at least three advantages to using immunotherapy to fight cancer.

It appears to be effective and doesn’t involve toxic chemicals. It may also continue to work even after treatments have stopped.

Lichtenfeld noted that between 35 and 40 percent of patients with advanced melanoma now respond positively to immunotherapy drugs like Keytruda. He said that percentage was closer to 0 percent less than a decade ago.

Dr. Hideho Okada, a professor in neurological surgery at the University of California San Francisco (UCSF), said those numbers are encouraging and a good sign for the future.

“The data speaks for itself in terms of survivor outcome,” Okada told Healthline.

Immunotherapy is seen as a more efficient way to go after the disease because it trains the immune system to fight cancer cells.

“It’s our bodies that are fighting the cancer,” Dr. Lawrence Fong, a professor in the department of medicine at UCSF, told Healthline.

There is also evidence the therapy continues to work even after treatment is stopped. Fong said that’s because the T cells have been activated and can continue to seek out any future invading cancer cells.

Lichtenfeld added immunotherapy is also teaching medical professionals how both the immune system and cancer cells work.

“What’s really exciting is the quality of the science in this research,” he said.