Understanding Systemic mastocytosis

Systemic mastocytosis (SM) is a rare condition caused by the accumulation of mast cells in the body’s organs, such as the skin, bone marrow, liver, spleen and small intestines. Mast cells are an important type of immune cell that normally play a role in the body helping fight infection and triggering the allergic response. In SM, the body produces too many mast cells, causing symptoms throughout the body.

Types of SM

Systemic mastocytosis is classified into two types with five categories: advanced SM (aggressive SM, SM with associated hematologic neoplasm, and mast cell leukemia) and non-advanced SM (smoldering SM and indolent SM). Usually, indolent and smoldering SM are treated by a dermatologist or allergist, while advanced SM care is generally provided by a hematologist or oncologist. Up to ~95% of people (Garcia-Montero AC et al. Blood. 2006;108(7):2366-2372.) have a specific mutation (genetic alteration) in a gene called KIT. The mutation, known as KIT D816V, is believed to play a central role in the activation and accumulation of mast cells in people with systemic mastocytosis. Depending on the subtype of SM, symptoms and treatments can vary.

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Advanced SM

In advanced systemic mastocytosis, the growth and activation of mast cells leads to potentially debilitating and life-threatening symptoms. Systemic symptoms may lead to organ damage, including but not limited to: low blood counts, malabsorption (unable to absorb nutrients) from gastrointestinal symptoms, chronic skin lesions, and dysfunctions in the liver, lungs, and bone.

There are three different subtypes of advanced SM – aggressive SM, SM with an associated hematological neoplam and mast cell leukemia.

Indolent and Smoldering SM

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People with indolent and smoldering systemic mastocytosis can experience severe symptoms which often present as severe allergies, but can include rashes, GI problems, fatigue, “brain fog,” unexplained anaphylaxis, bone pain, osteoporosis and more. Smoldering SM may have greater likelihood of progressing to advanced disease.

Talk to your healthcare provider if you think you or someone you know might have SM.

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Clinical Trials for Systemic Mastocytosis

At Blueprint Medicines, we are conducting multiple studies researching an investigational drug called avapritinib to potentially treat systemic mastocytosis. If you or someone you know may be interested in this research, please explore the following clinical trials to learn more.

Pathfinder Clinical Trial logo


An open-label clinical trial of investigational
avapritinib for people with advanced systemic mastocytosis.

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A double-blind clinical trial of investigational avapritinib versus placebo
for people with indolent systemic mastocytosis.

The PATHFINDER and PIONEER clinical trials are currently being conducted at trial sites around the world.

Travel support may be available to eligible study participants. More information about travel support will be provide by the study site during the screening process.

Avapritinib is currently being studied in systemic mastocytosis and is not approved by the U.S. Food & Drug Administration (FDA) or any other healthcare authority as safe or effective for use in this indication.