The Food and Drug Administration has issued a draft guidance saying that “pivotal treatment” for Pfizer’s leukemia drug Gleevec — including its benefit outweighing side effects — should only be given to adults with chronic myeloid leukemia, a rare form of cancer, rather than adults and children with newly diagnosed or very rapidly progressing acute myeloid leukemia, a more common form of the disease.

Women with regular contraception should also have access to the drug, which boosts the number of white blood cells in their bodies, according to the agency.

As with the preliminary assessment that the FDA released in January, the final guidance does not provide guidance as to the length of approval for use in patients. The agency has two weeks to decide whether to accept or deny the agency’s draft guidance.

“In the FDA’s current thinking, using Gleevec in front-line therapy in myeloid leukemia patients with CML is not an effective alternative to curative therapy,” the agency wrote. “What is of concern is that the lack of long-term safety and efficacy data available for this therapeutic option serves to compromise the long-term benefit in the context of patient survival.”

The agencies’ Feb. 19 draft guidance concluded that using Gleevec in children and adults under age 6, or women with regular contraception, might not increase the chance of long-term health benefits.

Several cancer care experts, and several patients, expressed frustration in their responses to the draft guidance. The Boston Globe reported on April 4 that one patient, Trisha Kramp, responded on Twitter, “I’m done wasting my efforts.”

Many patients with CML do not respond to other treatment options, so some have taken Gleevec for years to extend their lives. One study published in 2015 found that it doubled patients’ survival, compared with the typical survival rates for CML patients, which were at or near 15 years with no additional treatment. (The study did not seek to compare Gleevec to drugs that have newer or longer-term survival rates.)

The agency’s draft guidance suggested that, for some patients, “there is a reasonable expectation that the long-term benefit of treatment with Gleevec outweighs the risk of drug therapy.”

The regulatory group has not accepted those same assumptions for most patients with CML.

“The FDA expects any future decision to be based on evaluating the benefits and risks of the Gleevec product in front-line therapy and substantially extending the standard of care for myeloid leukemia,” the agency wrote.

Pfizer had not responded to requests for comment about its remarks at the advisory committee meeting on May 3.