Blueprint Medicines has reported positive data from the Phase II PIONEER trial evaluating avapritinib in patients with indolent systemic mastocytosis (SM).

Avapritinib (AYVAKIT) is a kinase inhibitor designed to selectively bind and inhibit D816V mutant KIT, which acts as a major cause for SM in about 95% of patients.

Part 1 of the study observed that subjects treated with avapritinib showed a statistically significant mean decline of about 30% in total symptom score (TSS) at 16 weeks, as measured by the Indolent SM Symptom Assessment Form (ISM-SAF).

Consistent improvements across objective measures of mast cell burden and patient-reported quality of life were noted in subjects treated with avapritinib.

Avapritinib was found to be well-tolerated, with no patients discontinuing treatment due to adverse events.

Blueprint Medicines chief medical officer Andy Boral said: “Avapritinib was specifically designed to inhibit D816V mutant KIT, with the goal of delivering transformative benefit to patients.”

“In indolent SM, these placebo-controlled data are the first to show consistent clinical activity across multiple measures of disease, from mast cell burden to clinical outcomes and quality of life.”

Based on the results from Part 1 of the study, 25mg once daily (QD) is selected as the recommended Part 2 dose (RP2D) of the PIONEER Phase II trial.

Avapritinib is currently approved by the US Food and Drug Administration (FDA) for the treatment of adults with unresectable or metastatic gastrointestinal stromal tumour (GIST) harbouring a PDGFRA exon 18 mutation, including PDGFRA D842V mutations.

Blueprint Medicines is working on the clinical development programme focused on the indication in advanced, smouldering and indolent SM, along with multiple areas of GIST treatment.

SM is a rare disease driven by the KIT D816V mutation. Anaphylaxis, pruritis, brain fog, maculopapular rash, bone pain and fatigue are among the associated symptoms of the disease.