A rare slowly progressive form of systemic mastocytosis (SM) characterized by gradual accumulation of neoplastic mast cells in the visceral organs. Patients typically present with splenomegaly hypercellular marrow and in most cases urticaria pigmentosa-like skin lesions.
Data from Orphanet are used to provide information on a disease's name, synonym(s), and overview. Reference: Access aggregated data from Orphanet at Orphadata. Orphadata: Free access data from Orphanet. © INSERM 1999. Available on http://www.orphadata.org. Data version April 2026
Newly diagnosed with
Smoldering systemic mastocytosis?
Our RARE Concierge Services Guides are available to assist you by providing information, resources and connections as you navigate your rare disease journey.
Advocacy Organizations
Super T’s Mast Cell Foundation
To increase awareness through resources, education and support for the mast cell diseases community, while also providing financial assistance to patients.
The Mast Cell Disease Society (TMS)
We are dedicated to providing multi-faceted support to patients, families and medical professionals in our community and to leading the advancement of knowledge and research in mast cell diseases through education, advocacy and collaboration.
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Clinical Trials
For a list of clinical trials in this disease area, please click here.