Systemic mastocytosis is a disorder caused by clonal mast cell proliferation and release of mast cell mediators including tryptase. As a result, mast cell numbers may increase and affect target organs including the dermis (maculopapular cutaneous mastocytosis/urticaria pigmentosa, flushing), gastrointestinal tract (abdominal pain, diarrhea), skeletal system (osteoporosis), hematological system (anemia, thrombocytopenia), and spleen and liver (organomegaly). Patients with indolent (non-aggressive) systemic mastocytosis (ISM) are not candidates for cytoreductive therapy and are generally treated with symptomatic therapy that only partly decreases symptoms. There is, however, a documented association between severity of mastocytosis and elevated serum levels of interleukin (IL)-6. Furthermore, mast cells have been shown to double their rate of division and exhibit increased reactivity and release of mediators when cultured in the presence of IL-6. In addition, in an animal model of mastocytosis, anti-IL-6 has been shown to slow disease progression. In this study, adults with ISM will thus be randomized and treated with sarilumab, a recombinant monoclonal antibody directed against the IL-6 receptor, or receive placebo. Sarilumab is marketed in the United States as Kevzara (Sanofi/Genzyme \[Cambridge, Massachusetts, USA \]) and is approved by the Food and Drug Administration for the treatment of rheumatoid arthritis. Binding of sarilumab to the IL-6 receptor inhibits IL-6-associated human mast cell signaling and proliferation with a resultant decrease in proliferation and reactivity (decreased mediator release), and therefore is a rational choice for the treatment of ISM.
In this study, participants will be randomized with approximately half of the participants receiving study drug, which will be administered at 200 mg via subcutaneous (SC) injection once every 2 weeks (Q2W) for a total of 16 weeks. The other participants will receive a placebo administered via SC injection Q2W for 16 weeks. Participants will return for a follow-up visit 2 weeks after the final dose (treatment peak), and then again 12 weeks later. Evaluations at study visits will include quality of life and symptom assessments and measurement of serum tryptase levels. Bone marrow examination will be performed at the onset and conclusion of the study. After the week 28 visit, all participants will have the option to continue sarilumab for 52 more weeks, at 200 mg administered via SC injections. Participants will continue to be monitored on a regular basis for safety concerns, as instructed in the study drug s package insert.
