Midostaurin in Indolent Systemic Mastocytosis

Inclusion Criteria: * Patients with Indolent Systemic Mastocytosis (ISM) or Smouldering Systemic Mastocytosis (SSM) according to the WHO criteria * Presence of the D816V c-KIT mutation * Serum tryptase \> 20 mg/l * Serious mediator-related symptoms that cannot be controlled by H1 and H2 blocking drugs. Symptoms will be scored by an adapted MSAF (mastocytosis symptom assessment form) with at least: * a pre-study score of 4 or more on 3 non-related items, * or a pre-study score of 5 or more on 2 non-related items. * one item from the scoring list can be replaced by flushes 7 or more per week or anaphylactic attacks 1 or more per week. * Age \>18 years * Willingness to apply optimal contraceptive measures (double barrier method, both men and women) for women below the age of 55, men at all ages; for both: if sexually active. * Written informed consent Exclusion Criteria: * Aggressive systemic mastocytosis, mast cell leukemia, or ASM with or without accompanying non-clonal related non-mast cell disorder (SM-ANHMD). * Any known other present malignancy, non-melanoma skin cancers excluded * History of malignancy within the last 5 years, non-melanoma skin cancers excluded * Any serious comorbidity interfering with therapy compliance and follow-up compliance * Pregnancy * Patients not willing or who are not able to comply with contraceptive measures