A new cumulative analysis from the PIONEER trial indicates avapritinib remains effective and well-tolerated when taken by patients with indolent systemic mastocytosis (SM) over longer periods, according to a recently published abstract in Clinical Lymphoma Myeloma and Leukemia.
The PIONEER trial aimed to evaluate avapritinib, a selective KIT D816V inhibitor, in patients with indolent SM. Its first two phases included randomized dose-finding and placebo-controlled segments, followed by a long-term extension (part 3) allowing open-label avapritinib treatment for up to five years. This structure allowed researchers to study its effectiveness and safety in the short term, and also monitor its long-term benefits and risks.
Over 220 patients received avapritinib 25 mg once daily or a placebo during the randomized phases, with placebo recipients later crossing over to avapritinib. Median treatment duration reached 35 months. Nearly half of participants took avapritinib for at least three years, with some extending to five years.
The results showed avapritinib had long-term benefits, with sustained improvements in total symptom scores and quality of life metrics through three years of follow-up. Patients reported lasting reductions in disease burden. These improvements persisted across years of treatment, highlighting the chronic benefit of targeting KIT D816V directly.
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The safety profile of avapritinib remained stable over extended follow-up. No new safety concerns were found compared to earlier research. Most treatment-related adverse events (TRAEs) were mild to moderate. Edema (swelling) was the most frequent, generally emerging within the first four months of treatment and remaining low in severity. Severe adverse events were rare, with only 1% of patients experiencing serious TRAEs and 3% discontinuing treatment due to side effects.
“Longer follow-up of patients with ISM in the PIONEER trial, including some on avapritinib for up to 5 years, demonstrates that prolonged avapritinib therapy continues to be effective and generally well tolerated,” the authors wrote.
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