CHICAGO — For the first time, a major study shows that a drug targeting the body’s disease-fighting immune system may improve survival for the most common form of lung cancer.

These newer kinds of drugs have transformed treatment of melanoma, the deadliest kind of skin cancer. Studies presented at a conference May 29 suggest these “immune therapies” can play a broader role in more common cancers.

Doctors also may have found a way to help predict which patients would respond best to one of these newer treatments, according to research presented at the Chicago meeting. Immune therapy drugs are aimed at helping the body’s immune system recognize and attack cancer.

The lung cancer study tested Bristol-Myers Squibb’s Opdivo, which blocks a protein that prevents the immune system from attacking cancer cells. It worked better than chemotherapy for patients with a form of non-small cell lung cancer.

Opdivo, also called nivolumab, was approved in March for a less common form of lung cancer, and late last year for melanoma. Two other immunotherapies are approved for melanoma — Keytruda and Yervoy.

“These drugs are among the most promising drugs that have come along” in many years, said Dr. Richard Schilsky, chief medical officer for the American Society of Clinical Oncology, the meeting’s organizer.

Any success against lung cancer is considered welcome. Patients are often diagnosed when the disease is advanced. It’s the No. 1 cancer killer in the country.

In the new study, almost 600 patients were assigned to receive infusions of Opdivo or the chemotherapy drug docetaxel every two weeks. Median survival was just over 12 months for Opdivo patients versus about nine months for chemo patients. That might seem unremarkable, but long-term survival chances are generally slim for these patients. Tumors shrank in almost 20 percent of Opdivo patients versus about 12 percent of the others.

“This is a huge step forward for treatment but we have a long way to go to be able to personalize this type of therapy,” said Dr. Julie Brahmer.