Efficacy of Omalizumab in Indolent Systemic Mastocytosis

BACKGROUND: Systemic mastocytosis (SM) comprises a heterogeneous group of disorders characterized by the proliferation of clonal mast cells in skin and various internal organs. Omalizumab is an established, labelled therapy for allergic asthma and chronic urticaria, but its experience in the efficacy of SM is limited. METHODS: A retrospective analysis of 6 patients diagnosed with indolent SM treated with omalizumab at St. Michael's Hospital between 2009 and 2018 is described. Reported frequency of anaphylaxis, baseline and follow-up tryptase levels, and SM-related symptoms were captured to measure the control of the disease. RESULTS: Of the 5 patients who had experienced unprovoked anaphylaxis prior to treatment with omalizumab, 3 had no further episodes of anaphylaxis following initiation of omalizumab, while the remaining 2 patients had milder multisystem reactions. Significant improvement in cutaneous symptoms was also observed. CONCLUSION: These data suggest that omalizumab provides benefit to patients with SM who remain highly symptomatic in spite of treatment with conventional therapies.