Omalizumab and Systemic Mastocytosis: A Single Centre Case Series

Systemic Mastocytosis (SM) represents a group of clonal disorders in which mast cells accumulate in one or more organ systems. Omalizumab is an off-label subcutaneously administered mast cell stabilizer which is frequently used to treat anaphylaxis. Changes in levels of tryptase, a mediator which marks the activity of the mast cell, affirms the response of omalizumab. We wanted to explore the use of omalizumab in controlling SM. This is a retrospective, descriptive case series of 5 patients (n=5) being treated with omalizumab for their SM. Patients were eligible if they had bone marrow biopsy confirmed SM, based on the 2016 WHO criteria. Electronic medical records were reviewed by two independent reviewers (CS, CS) to identify SM symptoms and tryptase levels prior to the initiation of ketotifen (≤6 months prior) and again post-initiation (4-8 months post). The Brown anaphylaxis score was used to record severity of anaphylaxis (scores of 3: severe life-threatening reactions; 2: moderate systemic involvement; 1: no systemic involvement). 100% of patients responded to treatment with responses ranging from 17% to 100% improvement in mastocytosis-linked symptoms. Both 2 patients whose tryptase levels were available at baseline and follow-up saw reduction in levels; one patient from 134 ng/mL to 84. 3/5 patients improved from severe anaphylaxis (score of 3) to mild (1). 2 patients remained at moderate (2). Omalizumab appears to effectively manage SM symptoms as well as lowers tryptase levels.