A new study has analyzed data from the multicenter phase 1 EXPLORER trial and confirmed the sustained efficacy and safety of avapritinib in patients with systemic mastocytosis (SM).

However the study, published in Blood, found that the median overall survival was not reached at nearly 4 years of follow-up.

“Avapritinib, an oral, highly selective inhibitor of KIT D816V, is approved in the USA for treatment of adult patients with advanced SM (AdvSM), and in Europe after ≥1 prior systemic therapy,” the authors wrote. “Here we present long-term analyses from EXPLORER showing sustained efficacy, deepening responses, mature progression-free survival (PFS), updated overall survival, and consistent safety profile.”

The research team analyzed data on 69 adult patients with AdvSM undergoing avapritinib therapy once daily at 30 to 400 mg. The main outcome measures were maximum tolerated dose and recommended phase 2 dose, safety, and tolerability.

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Secondary outcome measures included overall response rate, changes in disease burden, progression-free survival, and overall survival.

The results as of April 2022 showed, after almost 4 years of follow-up, an ongoing survival benefit without reaching the median overall survival. Patients on avapritinib had rapid and durable responses to the therapy, with reductions in objective measures of disease burden. Only 25% of the participants had disease progression.   

Avapritinib was well-tolerated by the participants, and the safety profile was consistent with that found in previous studies. The most common adverse events were periorbital edema, anemia, thrombocytopenia, nausea, and peripheral edema. Most of the patients had dose reductions (73%) or treatment interruptions (83%) due to adverse effects, but this had no negative impact on the clinical efficacy of the therapy.


DeAngelo D, Radia DH, George TI, et al. An updated analysis on safety and efficacy of avapritinib in patients with advanced systemic mastocytosis from the EXPLORER clinical study: long-term efficacy and safety. Blood. Published online November 15, 2022. doi:10.1182/blood-2022-167593