A new study has found that 200 mg of avapritinib once a day is effective and well tolerated among treatment-naïve patients with advanced systemic mastocytosis (SM).

The study, presented orally at the 64th ASH Annual Meeting and Exposition in New Orleans, Louisiana, was based on analyses of patients with confirmed advanced SM included in the PATHFINDER clinical trial.

“Data from the multi-center, international, phase 1 EXPLORER and phase 2 PATHFINDER clinical studies demonstrated that responses to avapritinib treatment were rapid, deep, and durable regardless of prior therapy, advanced SM subtype, or presence of high-risk mutations,” the authors wrote. “Here we present analyses from patients with advanced SM treated with avapritinib as first-line therapy in PATHFINDER.”

The analyses included 107 patients with advanced SM who had no previous antineoplastic treatment. They initiated 200 mg of avapritinib once daily as part of the PATHFINDER study, where the primary endpoint was the overall response rate as defined by modified International Working Group-Myeloproliferative Neoplasms Research and Treatment-European Competence Network on Mastocytosis response criteria.

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Secondary endpoints were mean change from baseline in bone marrow mast cell burden, serum tryptase, blood KIT D816V variant allele fraction, spleen volume, duration of response, time to response, and overall survival and safety, among other measures.

The results revealed an overall survival of 96% at 12 months and 88% at 24 months, as well as reductions in measures of disease burden of 50% or more. Complete clearance of neoplastic mast cell aggregates was observed in 63% of the participants. Common adverse events included periorbital edema, thrombocytopenia, and anemia. However, the medication was generally well tolerated; only 10% discontinued the therapy due to treatment-related adverse events.


Radia D, Gotlib J, Drummond MW, et al. Avapritinib as first-line therapy in patients with advanced systemic mastocytosis: efficacy and safety from the pathfinder clinical study. Oral Abstract. 64th ASH Annual Meeting and Exposition, New Orleans, Louisiana. December 11, 2022.