A Non-Interventional Study in Participants With Indolent Systemic Mastocytosis (ISM) in Germany

Inclusion Criteria: * Participants is starting avapritinib treatment at the HCP's discretion as part of their routine care (for ISM with moderate to severe symptoms inadequately controlled with symptomatic treatment) and in accordance with approved SmPC. Exclusion Criteria: * Participant with a potential increased risk for intracranial hemorrhage including those with a history of vascular aneurysm, intracranial hemorrhage, cerebrovascular accident within the prior year, or severe thrombocytopenia. * Participant who has previously taken avapritinib as a commercial drug or as part of a clinical study.