Cem Akin, MD, PhD, Professor, Allergy and Immunology at the University of Michigan, discusses with CheckRare systemic mastocytosis, and the results of the phase 2 PIONEER study, which tested the tyrosine-kinase inhibitor avapritinib (Ayvakit) against placebo in symptomatic patients. These results were presented at the 2026 AAAAI meeting in February 2026.
Mastocytosis is an incurable, heterogeneous disorder that is classified into two forms: cutaneous mastocytosis (seen in children) and systemic mastocytosis (mainly seen in adults). The systemic form is associated with an acquired (not inherited) genetic variant called KIT D816V, which is found in stem cells of more than 95% of affected patients.
Less than 15% of patients with systemic mastocytosis have advanced disease; the rest have nonadvanced types. Advanced disease is associated with decreased life expectancy and survival, whereas the other forms are not. However, patients with the more-common indolent or smoldering forms present with chronic symptoms (e.g., skin lesions, gastrointestinal and neurocognitive symptoms, osteopenia/osteoporosis). These symptoms are most often managed with antihistamines, leukotriene inhibitors, and mast-cell stabilizers. Due to the heterogeneity of the disorder, symptom burden may be relatively low or great; it can truly affect patients’ quality of life, daily activities, social life, and personal relationships.
Dr. Akin described the phase 2 PIONEER study, a double-blind, placebo-controlled investigation to evaluate the safety and efficacy of a selective tyrosine-kinase inhibitor avapritinib, which targets the KIT mutation. PIONEER had three components: (1) a dose-finding investigation, which settled on 25 mg/day orally as the primary dose tested; (2) the 6-month, randomized, placebo-controlled trial in patients with symptoms that were inadequately controlled with other medications; and (3) a long-term (follow-up is ongoing, up to 5 yr), open-label extension trial, which included switching the patients who receive placebo previously to active treatment with avapritinib.
The randomized, controlled portion of PIONEER proved that the avapritinib was clinically effective, as shown by various primary and secondary endpoints, including clearance or clinical improvement in skin lesions, reduction in symptoms scores, lower mast-cell load, and improvements in other biologic markers of the disease. Dr. Akin pointed out that the extension portion of PIONEER showed that these benefits were durable for up to 5 years with continued use.
In terms of safety, no additional safety concerns were observed through the extended follow-up phase. Peripheral and periorbital dema was seen in about 10% of patients (not serious, and no patient discontinued as a result).
In the open-label extension, a group of patients were allowed to increase their dose to 50 mg/mg based on their symptom burden, mast-cell markers, and the perceived patient response to the medication. Patients with the higher dose continued to improve symptomatically, with no additional safety concerns (their follow-up was up to 1 yr at this point).
Dr. Akin said that the PIONEER study provided confidence that the mutation is in fact the main driver of the disease, and if we can suppress expression of the mutation, we can change the outcome of systemic mastocytosis. “When disease markers and symptoms improve, we expect the response to be durable,” he stated. “Avapritnab kills the stem cells carrying the mutation, and when therapy is stopped, we expect that the systemic mastocytosis symptoms and markers will return. It is important to make the point that this is a chronic therapy.” PIONEER provided the reassurance that avapritinib is safe and effective over the long term.
CHAPTERS
Introduction 00:00
Mastocytosis Overview 00:42
Burden of Disease 2:30
PIONEER Clinical Trial Design 3:37
Four-Year Follow-Up Data 5:13
Durability of Symptom Improvements 8:40
GI Symptoms, Bone Health, and Other Manifestations 9:31
Effect of Ayvakit on Underlying Disease 11:58
Selection of Patients 13:39
Unanswered Questions for Future Studies 17:12
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