An experimental drug that boosts the body's immune system has helped some patients with advanced melanoma keep their disease in check for several years, a new study indicates, Newsmax Health reports.

Researchers think the drug, which is called nivolumab, may help reset the immune system so that as a tumor adds new cells, the immune system is able to clear them away.

"We're hypothesizing that we have reset the balance between the immune system and the tumor," said study author Dr. Suzanne Topalian, director of the melanoma program at Johns Hopkins University in Baltimore.

An expert who was not involved in the study called the results "remarkable."

Some tumors make molecules that switch off the immune system's ability to recognize and kill cancer cells. Nivolumab essentially releases the brakes a cancer has applied to immune attack cells, restoring the body's ability to clear the disease.

All of the patients in the study had the dangerous skin cancer known as advanced melanoma, and 80 percent had tumors that had spread to other organs. 

People in the study received intravenous doses of the drug every two weeks for up to two years. Thirty-three patients who took the drug saw their tumors shrink by at least 50 percent on the medication. In a few cases, the masses disappeared completely.

Another seven patients had stable disease, meaning their cancer didn't get worse or better for at least six months.

The other 67 patients had mixed responses -- meaning some of their tumors grew while others shrank, or their tumors grew despite treatment.

Overall, 62 percent of patients who enrolled in the trial were still alive a year later, and 43 percent were still alive after two years.