Drug Shows Promise Treating Rare Immune Cancer

New treatment for mast cell leukemia could improve quality-of-life and overall survival.

An investigational multi-kinase inhibitor drug may be effective in significantly prolonging survival and improving quality-of-life for people with advanced mastocytosis.

Mastocytosis is a rare immune disease that causes the body to produce to many abnormal mast cells, which control allergic and inflammatory responses. Advanced mastocytosis, called mast cell leukemia, is the deadliest subtype of the disease and individuals live less than 6 months after diagnosis.

At this time, there is only one FDA-approved drug to treat advanced mastocytosis, called imatinib, which is designed to block the action of the cellular protein tyrosine kinase receptor. However, a majority of patients with advanced mastocytosis have a mutation in the gene D816V KIT, which prevents them from responding to treatment with imatinib.

In a study published in the New England Journal of Medicine, researchers first began their research on the new drug midostaurin. A woman with mast cell leukemia was given midostaurin under the FDA’s compassionate use policy.

“Midostaurin was being evaluated in a clinical trial for a different disease, acute myeloid leukemia,” said researcher Tracy George, MD. “And this lady with mast cell leukemia remarkably improved within weeks, within days.”

These findings caused researchers to begin a small clinical trial to test midostaurin in advanced mastocystosis patients. Once the preliminary results were shared at an international conference, the trial was expanded into an international clinical trial.

Although the clinical trial included treatment for 3 subtypes of advanced mastocytosis, it took several years to enroll enough patients into the trial. This is because the disease is so rare, and only affects approximately 1 person in 10,000.

There were 16 people in the trial who had mast cell leukemia. Despite the small size of the trial, the results were astounding, according to the study authors.

“This is the first drug that’s shown to be effective in this very rare disease,” George said.

The results of the study showed that those with advanced mastocytosis lived an average of 28 months longer, with the average including 40% of individuals unresponsive to midostaurin. The 60% of patients who did respond to the drug did achieve a response within 2 to 3 months of starting treatment, however.

“For those patients who did respond, their median survival has not been reached,” George said. “So that means [some are] living, which is unbelievable.”

There were little to no side effects, with a few people who experienced mild adverse events, such as nausea, vomiting, and diarrhea.

On the heels of these results, scientists around the globe are now studying how midostaurin affects mast cells, and how to combine it with other drugs in order to create an even more potent and effective treatment. There have also been clinical trials opened that are testing midostaurin for controlling symptoms in people with indolent mastocytosis, while more research is in the planning stages to evaluate midostaurin in the treatment of asthma, allergies, and skin diseases.

“I do think this [mastocytosis] is under-diagnosed,” George said. “Even though patients with advanced mastocytosis are rare, indolent [mastocytosis] is more common. And there are lots of diseases of which unhappy mast cells are a pathogenesis.”