PIONEER Skin Assessments Supplemental Material

Background:
Indolent systemic mastocytosis (ISM), a clonal mast cell disease driven by the KIT D816V mutation, can often cause debilitating dermatologic symptoms.
Objective:
Assess improvement of ISM-related skin manifestations after treatment with avapritinib, a highly selective KIT D816V inhibitor, vs placebo in Part 2 of the PIONEER study (NCT03731260).
Methods:
Patients with moderate-to-severe ISM received avapritinib 25 mg once daily (n=141) or placebo (n=71). Endpoints included skin lesion area and pigmentation at week 24, skin mast cell burden, and change in symptoms.
Results:
Mean percent reduction in lesional surface area was −36.6% with avapritinib vs −1.8% with placebo in the most affected area; 86% vs 0% had improved skin lesion color. Mean percent change in skin mast cell burden decreased with avapritinib (−22.1%) vs placebo (10.1%). Avapritinib vs placebo significantly improved skin symptom domain score (mean change −7.2 vs −2.8; p<.0001), including the individual skin symptoms itching, flushing, and spots. Avapritinib was well tolerated.
Limitations:
Photography was optional, so analysis population for lesion area and color were smaller (n=111) than the overall study population (n=212).
Conclusion:
Avapritinib treatment improved dermatologic symptoms, decreased skin lesion size, normalized skin lesion color, and reduced skin mast cell burden in patients with ISM.

These data are the supplemental material for the primary publication of PIONEER Skin Assessments in JAAD.