Treatment of Indolent and Advanced Systemic Mastocytosis

Management of Indolent and Smoldering SM is focused on preventing anaphylactic reactions and identifying and avoiding symptom triggers. Skin and gastrointestinal symptoms are managed with H1- and H2-antihistamines. When skin symptoms are not adequately controlled, leukotriene antagonists and oral psoralen combined with ultraviolet therapy may be added. Proton pump inhibitors, sodium cromolyn, and oral corticosteroids may be added for gastrointestinal symptoms. Patients should be prescribed self-injectable epinephrine and trained to treat recurrent cardiovascular symptoms or anaphylaxis. Depression and cognitive impairment require a psychiatric evaluation for tailored treatment. Bone involvement is managed with bisphosphonates and eventually interferon. Omalizumab is effective on all vasomotor symptoms, including anaphylaxis, but not on respiratory, musculoskeletal, and neuropsychiatric symptoms. A cytoreductive treatment is not recommended unless anti-mediator therapy has failed. Venom immunotherapy is mandatory for patients with Hymenoptera venom allergy. There is no curative option for patients with advanced SM. The available therapeutic options include tyrosine-kinase inhibitors and cladribine, with variable duration and extent of response. Imatinib mesylate was the first drug approved for SM lacking the cKIT D816V mutation; dasatinib and nilotinib are ineffective. Midostaurin is active on both wild-type and mutant cKIT D816V, while Avapritinib is a selective cKIT D816V inhibitor: they are approved for the treatment of advanced SM. Cladribine is a purine analog with significant activity against monocytes that were thought to have a common progenitor with mast cells. Allogeneic stem cell transplantation is usually performed in younger selected patients.