# PATHFINDER: efficacy and safety of avapritinib in advanced systemic mastocytosis (phase 2 interim analysis)

Source: https://onco.cc/key-papers/paper-pathfinder-avapritinib-advanced-systemic-mastocytosis-nat-med-2021/  
OnCo record `paper-pathfinder-avapritinib-advanced-systemic-mastocytosis-nat-med-2021` (Key paper). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

The confirmatory trial of avapritinib in advanced systemic mastocytosis again showed responses in three quarters of patients, with the drug clearing marrow mast cells and normalising tryptase in many, and it became the standard first-line targeted therapy.

## Summary

Open-label single-arm phase 2 trial of avapritinib 200 mg daily in adults with advanced systemic mastocytosis; the pre-specified interim analysis included 62 patients, 32 evaluable for response.

The overall response rate was 75 percent, with complete remission with full or partial haematological recovery in 19 percent, and rapid reductions in marrow mast cells, serum tryptase and KIT D816V allele fraction; quality of life improved. Patients with platelets under 50,000 per microlitre were excluded to avoid intracranial bleeding.

## Fields

- Kind: Key paper
- Last checked: 2026-09-18
- Journal: Nature Medicine
- Year: 2021
- DOI: 10.1038/s41591-021-01539-8
- Authors: Gotlib J, Reiter A, Radia DH, et al.
- Findings: Overall response 75 percent in evaluable patients at the interim analysis, with complete remission with full or partial haematological recovery in 19 percent.; Marrow mast cell burden and serum tryptase fell in most patients.
- What it means: Avapritinib is the preferred first targeted therapy for advanced systemic mastocytosis in patients with adequate platelet counts.
- Caveats: Interim analysis of a single-arm trial.; Excluded patients with severe thrombocytopenia, who are common in mast cell leukaemia and have few options.

## Sources

- Nat Med 2021: https://doi.org/10.1038/s41591-021-01539-8
- PubMed: https://pubmed.ncbi.nlm.nih.gov/34873345/

## Connected records

- cancers: [Advanced systemic mastocytosis (aggressive SM, SM with an associated haematological neoplasm, mast cell leukaemia)](https://onco.cc/cancers/advanced-systemic-mastocytosis/)
- drugs: [Avapritinib](https://onco.cc/drugs/avapritinib/)
- journals: [Nature Medicine](https://onco.cc/journals/nature-medicine/)

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