Federal regulators Friday approved the first drug shown to prolong the lives of patients with advanced skin cancer.

The Food and Drug Administration announced approval of the drug Yervoy, which is also known as ipilimumab, for late-stage melanoma, the most dangerous type of skin cancer.

About 68,130 new cases of melanoma were diagnosed in the United States and about 8,700 people died from the disease in 2010, according to the National Cancer Institute.

“Late-stage melanoma is devastating, with very few treatment options for patients, none of which previously prolonged a patient’s life,” said Richard Pazdur, director of the FDA’s Office of Oncology Drug Products in the Center for Drug Evaluation and Research. “Yervoy is the first therapy approved by the FDA to clearly demonstrate that patients with metastatic melanoma live longer by taking this treatment.”

Yervoy, which is made by Bristol-Myers Squibb in New York, is a so-called monoclonal antibody. It works by blocking a molecule known as cytotoxic T-lymphocyte antigen or CTLA-4, which is believed to play a role in hampering the ability of the body’s immune system to fight cancerous cells. By blocking CTLA-4, the immune system can better “recognize, target, and attack cells in melanoma tumors,” the FDA said in a statement announcing Yervoy’s approval.

Yervoy was studied in 676 patients whose melanoma had spread or could not be removed surgically and had stopped responding to other treatments. The patients received Yervoy plus an experimental tumor vaccine called gp100, Yervoy alone, or the vaccine alone. The patients who received the combination of Yervoy plus the vaccine or Yervoy alone lived an average of about 10 months, while those who received only the vaccine lived an average of 6.5 months.

The drug can, however, cause a variety of side effects, including fatigue, diarrhea, rashes, and colitis. About 13 percent of patients experienced severe, potentially fatal immune system reactions, requiring them to stop treated with Yervoy and take steroids. Because of this, the drug was approved with the requirement that doctors and patients understand the risks.

Bristol-Myers said it would charge $120,000 for a complete course of treatment, which consists of four infusions given over three months.

While the treatment is not a cure for the disease, the approval was hailed as a milestone in treating melanoma.

“While ipilimumab, on average, extended the lives of patients by four months, there is also a group of patients who experienced a greater benefit and lived many months while being treated with this drug,” said F. Stephen Hodi, director of the melonoma treatment center at the Dana-Farber Cancer Institute in Boston, who studied the drug. “This is a big step in the right direction becuase it demonstrates that this class of drugs can benefit cancer patients.”

The approval was also welcomed by those advocating finding ways to harness the immune system to fight cancer.

“This is a landmark advance for several reasons,” said Thomas Gajewski, president of the Society for Immunotherapy of Cancer . “First, this is a completely new way to treat cancer, by blocking a negative regulator of the immune response. Second, it is the first drug ever to show improved survival of metastatic melanoma patients. And third, we learned that clinical responses to immune therapies such as this one can take time, requiring some patience. FDA approval of this drug further strengthens the case for cancer immunotherapy. We anticipate other novel immune therapies that will benefit patients with cancer over the coming years.”