CHICAGO (AP) — A study shows a new kind of drug for the deadliest form of skin cancer helped some patients survive for at least three years.

It’s a remarkable advance for patients who until recently faced dismal chances of living for more than a few months.

About 40 percent of the melanoma patients in the study were still alive three years later. The findings are for a drug marketed by Merck as Keytruda (kee-TROO’-duh), which targets the immune system.

It was one of the treatments given to former President Jimmy Carter, who was diagnosed last year with melanoma that had spread to his brain.

The study involved 655 patients and was released Wednesday in advance of an American Society of Clinical Oncology meeting next month in Chicago.