The federal health insurance program for the elderly moved Wednesday to pay for an expensive vaccine recently approved to treat men with advanced prostate cancer.

The Centers for Medicare and Medicaid Services proposed paying for the vaccine, known as Provenge, which costs $93,000 a patient. The proposal will be subject to public comment for 30 days, and a final decision will be issued 60 days after that.

“The evidence is adequate to conclude that” Provenge “ improves health outcomes for Medicare beneficiaries” with metastatic prostate cancer, “and thus is reasonable and necessary for that indication,” CMS said in announcing its decision.

Although Medicare is not supposed to take cost into consideration when making such rulings, the decision by CMS to launch a formal examination raised concerns among cancer experts, drug companies, lawmakers, prostate cancer patients and advocacy groups.

Provenge, which received Food and Drug Administration approval in April, is the latest in a series of new, high-priced cancer treatments that appear to eke out only a few more months of life, prompting alarm about their costs. Provenge appears able to extend patients’ lives by about four months.

Because men tend to be elderly when they receive diagnoses of advanced prostate cancer, Medicare’s decision will have a major effect on Provenge’s accessibility. Private insurers also tend to follow Medicare’s lead.

Medicare officials have said Provenge’s price tag was not an issue, and some outside experts said the agency was motivated more by questions about the vaccine’s effectiveness and concerns that it might be used “off-label” for purposes not specifically approved by the Food and Drug Administration.

In November, the Medicare Evidence Development and Coverage Advisory Committee endorsed the vaccine, saying there was sufficient evidence that Provenge could help extend patients’ lives. The committee, however, also voted that there was inadequate evidence that Provenge would help other kinds of patients, such as those who were either sicker than those studied to get Provenge approved or not as sick.

Medicare usually covers new cancer drugs once they have been approved by the FDA. The decision in June to scrutinize Provenge prompted several members of Congress to question the action. Supporters of the drug’s approval inundated the agency with hundreds of thousands of comments.

Provenge has long been controversial. The FDA delayed its approval in 2007. The rejection triggered outrage among patients, advocates and investors in Dendreon, the Seattle company that developed the drug. The campaign to win Provenge’s approval included anonymous death threats, accusations of conflicts of interest, protests, congressional lobbying and vitriolic Internet postings.

Prostate cancer strikes 192,000 men in the United States each year and kills about 27,000. The only therapies are surgery, radiation, hormones and the chemotherapy drug Taxotere.

Unlike standard vaccines, which are given before someone gets sick to stimulate their immune system to fight off infections, Provenge is a “therapeutic vaccine,” designed to spur the immune system to attack cancer cells in the body.