An Observational Study in Participants With Indolent Systemic Mastocytosis (ISM)

This is a Phase 4, non-interventional, observational study to collect detailed data on the clinical characteristics, clinical outcomes and medical management of ISM in real-world settings. The study will describe the demographic and clinical characteristics of ISM participants, including anaphylaxis and bone manifestations in ISM. Quality of life and disease control will be assessed through participant questionnaires. The study will also evaluate real world ISM treatment management, including use of avapritinib.

Inclusion Criteria: * Male or female adult participants (≥ 18 years of age) with a diagnosis of ISM according to the World Health Organization (WHO) diagnostic criteria * Participant is currently being treated or plans to be treated with symptom-directed therapies and/or avapritinib for ISM. Exclusion Criteria: * Participants with advanced systemic mastocytosis (AdvSM) or another associated hematologic neoplasm * Participants with smoldering systemic mastocytosis * Ongoing participation in interventional studies in systemic mastocytosis (SM) at the time of enrollment * Participants currently receiving treatment with a KIT inhibitor other than avapritinib at the time of enrollment.