Diagnosis and management of systemic mastocytosis in a community hematology setting.

Background: Systemic mastocytosis (SM) is a rare and potentially severe hematologic disorder characterized by the clonal proliferation of mast cells (MCs) into various organs. The clinical manifestations of advanced SM are caused by the uncontrolled release of cytokines and vasoactive amines from MC and disease-induced organ dysfunction. Patients with SM typically present with symptoms such as flushing, pruritus, diarrhea, and headaches, but outcomes following active treatment have not been well characterized. In this study, the clinical characteristics, treatment patterns, and natural history of an SM patient cohort diagnosed and treated within a community hematology network in the United States is described.

Methods: We identified 105 patients who were diagnosed and managed in one of 19 community hematology clinics up to an index date of 1 October 2022. Data collection included patient and disease characteristics, baseline biochemistry and hematology, SM diagnostic criteria being met, biomarkers tested, CD2 and/or CD25 expression in MCs as well as serum tryptase levels at presentation. Data abstraction also included supportive care drugs and anticancer therapy used, treatment response, reason for discontinuation, and overall survival by disease subtype.

Results: A total of 105 SM patients were identified who met the inclusion criteria. The specific SM subtypes were indolent (47.6%), aggressive (9.5%), SM with an associated hematological neoplasm (19.0%), MC leukemia (1.9%), and subtype not documented (21.9%). Regardless of subtype, approximately 62% of patients did not receive SM-directed active therapy. Only 26% of patients with indolent systemic mastocytosis (ISM) received treatment compared to 65.6% with advanced subtypes. Relative to ISM cohort, the relative risk of death in patients with the advanced SM subtypes was approximately 15 times greater (hazard ratio = 15.0; 95% confidence interval: 3.3 to 66.5).

Conclusions: SM patients present with multiple underlying symptoms, within various disease subtypes that are difficult to diagnose in a timely manner. As a result, many patients do not receive active drug therapy for their disease. Therefore, greater disease awareness is required as well as new tools for earlier disease detection.