Doctors classify systemic mastocytosis (SM) into several subtypes that fall into two broad groups: nonadvanced and advanced. The categorization is based on how the disorder affects the body.
Understanding the difference between nonadvanced and advanced SM can help those affected by the condition better understand their diagnosis and treatment options.
What is nonadvanced systemic mastocytosis?
Nonadvanced SM includes several forms of the disorder, most commonly indolent systemic mastocytosis (ISM) and smoldering systemic mastocytosis (SSM). In these subtypes, mast cells accumulate in the body but usually do not cause severe organ damage.
Learn more about SM signs and symptoms
People with nonadvanced SM often experience symptoms related to mast cell activation, such as:
- Flushing.
- Itching or hives.
- Abdominal pain, diarrhea or nausea.
- Headaches.
- Allergic reactions, including anaphylaxis.
- Bone pain or fatigue.
Although these symptoms can significantly affect quality of life, the underlying disease typically progresses slowly, and many people with nonadvanced SM go on to live normal or near-normal lifespans.
Treatment usually focuses on controlling symptoms and preventing mast cell activation. This may include antihistamines, medications that stabilize mast cells or treatments aimed at reducing gastrointestinal symptoms and allergies.
What is advanced systemic mastocytosis?
Advanced SM is less common, but a more serious form of the disorder. It includes several subtypes, such as aggressive SM, mast cell leukemia (MCL) and SM with an associated hematological neoplasm (SM-AHN).
The key difference is that in advanced SM, mast cells begin to damage organs. Examples can include:
- Liver damage or enlargement.
- Enlarged spleen with low blood cell counts.
- Severe bone damage or fractures.
- Malabsorption and significant weight loss.
- Bone marrow failure leading to anemia or other blood problems.
Advanced SM usually requires therapies aimed at reducing the number of abnormal mast cells, including targeted treatments that block the signaling pathways driving mast cell growth, stem cell transplantation and medications for blood cancers.
Because advanced SM affects the organs, it is more likely to shorten life expectancy.
Why classification matters
While both forms involve abnormal mast cells, nonadvanced and advanced SM behave very differently. Nonadvanced SM is primarily characterized by bothersome symptoms, while advanced SM is defined by organ damage and more aggressive disease.
Understanding which category a person falls into helps doctors estimate disease risk, monitor for complications and choose the most appropriate treatment strategy. For those living with the disorder, it can also provide important context about what to expect and how care may evolve over time.
Sign up here to get the latest news, perspectives, and information about SM sent directly to your inbox. Registration is free and only takes a minute.
