Efficacy and safety of avapritinib in advanced systemic mastocytosis: interim analysis of the phase 2 PATHFINDER trial

Nat Med. 2021 Dec;27(12):2192-2199. doi: 10.1038/s41591-021-01539-8. Epub 2021 Dec 6.


Advanced systemic mastocytosis (AdvSM) is a rare, KIT D816V-driven hematologic neoplasm characterized by mast cell infiltration and shortened survival. We report the results of a prespecified interim analysis of an ongoing pivotal single-arm phase 2 trial (no. NCT03580655 ) of avapritinib, a potent, selective KIT D816V inhibitor administered primarily at a once-daily starting dose of 200 mg in patients with AdvSM (n = 62). The primary endpoint was overall response rate (ORR). Secondary endpoints included mean baseline change in AdvSM-Symptom Assessment Form Total Symptom Score and quality of life, time to response, duration of response, progression-free survival, overall survival, changes in measures of disease burden and safety. The primary endpoint was successfully met (P = 1.6 × 10-9), with an ORR of 75% (95% confidence interval 57-89) in 32 response-evaluable patients with AdvSM who had sufficient follow-up for response assessment, including 19% with complete remission with full or partial hematologic recovery. Reductions of ≥50% from baseline in serum tryptase (93%), bone marrow mast cells (88%) and KIT D816V variant allele fraction (60%) were observed. The most frequent grade ≥3 adverse events were neutropenia (24%), thrombocytopenia (16%) and anemia (16%). Avapritinib demonstrated a high rate of clinical, morphological and molecular responses and was generally well tolerated in patients with AdvSM.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Clinical Trials, Phase II as Topic
  • Female
  • Humans
  • Male
  • Mastocytosis, Systemic / drug therapy*
  • Middle Aged
  • Pyrazoles / adverse effects
  • Pyrazoles / therapeutic use*
  • Pyrroles / adverse effects
  • Pyrroles / therapeutic use*
  • Triazines / adverse effects
  • Triazines / therapeutic use*


  • Pyrazoles
  • Pyrroles
  • Triazines
  • avapritinib

Associated data

  • ClinicalTrials.gov/NCT03580655