The MastAttack 107: The Layperson’s Guide to Understanding Mast Cell Diseases, Part 26

I answered the 107 questions I have been asked most in the last four years. No jargon. No terminology. Just answers.

34. What are the differences between the forms of systemic mastocytosis?

Indolent systemic mastocytosis

  • A form of SM in which the amount of mast cells produced in the bone marrow is excessive but not inherently dangerous to organ function.
  • Mast cells produced in the bone marrow are damaged.
  • These mast cells are released into the blood. While there are more mast cells than usual, there are not enough to overwhelm the blood.
  • There are fewer mast cells than in mast cell leukemia. There are often fewer mast cells than aggressive systemic mastocytosis or smoldering systemic mastocytosis.
  • The mast cells leave the blood and may enter organs inappropriately. Some patients do not have signs of too many mast cells being in an organ other than bone marrow.
  • The presence of mast cells in organ tissue can cause symptoms and medical signs but is not inherently dangerous to organ function.
  • It is not unusual for ISM patients to have typical mast cell symptoms and complications like anaphylaxis.
  • The lifespan for ISM is normal.
  • In indolent systemic mastocytosis, patients die from progressing to a more aggressive form of SM, such as MCL, ASM or SM-AHD.
  • Fatal anaphylaxis is always a risk with mast cell disease.

Smoldering systemic mastocytosis

  • A form of SM in which the amount of mast cells produced in the bone marrow is increasing to the point at which it might cause organ damage.
  • Mast cells produced in the bone marrow are damaged.
  • These mast cells are released into the blood. There are fewer mast cells than in mast cell leukemia. There are often fewer mast cells than aggressive systemic mastocytosis.
  • Mast cells leave the blood and enter organs in larger numbers than is normal. The presence of mast cells in these organs can cause symptoms and medical signs, like swelling of the liver.
  • Organ dysfunction can sometimes be corrected with surgery or certain medications.
  • It is not unusual for SSM patients to have typical mast cell symptoms and complications like anaphylaxis.
  • The lifespan for SSM is widely variable. One well known paper published survival of around ten years. However, many of the patients in this study were over 60 and age may have affected the average survival found in this group.
  • Patients with smoldering systemic mastocytosis are monitored to look for signs of significant organ dysfunction.
  • People with this diagnosis are considered to be possibly transitioning to a more serious form of systemic mastocytosis.
  • Smoldering systemic mastocytosis is the diagnosis that occurs between aggressive systemic mastocytosis and indolent systemic mastocytosis. It is thought of as the stage crossed when a patient with indolent systemic mastocytosis progresses to having aggressive systemic mastocytosis or mast cell leukemia.
  • In smoldering systemic mastocytosis, patients die from progressing to a more aggressive form of SM, such as MCL, ASM or SM-AHD.
  • Fatal anaphylaxis is always a risk with mast cell disease.

Aggressive systemic mastocytosis

  • A dangerous form of SM in which your bone marrow makes way too many damaged mast cells.
  • These mast cells are released into the blood. There are fewer mast cells than in the blood than in mast cell leukemia.
  • The mast cells leave the blood and go into various organs.
  • The presence and activation of the mast cells in the organs can affect organ function.
  • Over time, the presence and activation of mast cells in the organs can cause organ failure. This can sometimes be corrected with surgery or certain medications.
  • Typical mast cell mediator symptoms and complications like anaphylaxis are less common than in less serious types of SM.
  • The lifespan for ASM is much shorter than normal but is dependent upon response to treatment and which organs are involved. Older papers reference an average of 41 month survival but this has changed with more recent treatment options.
  • Generally, people with ASM live longer than those with MCL.
  • In aggressive systemic mastocytosis, patients die from the organ damage that has accrued over time by the presence and activation of mast cells in places they don’t belong.
  • Fatal anaphylaxis is always a risk with mast cell disease.

Mast cell leukemia

  • A very dangerous form of SM in which your bone marrow makes massive amounts of damaged mast cells.
  • These mast cells are released into the blood in overwhelming numbers.
  • The mast cells leave the blood and end up in various organs.
  • Specifically because of how many mast cells are present, mast cells invading the organs break up the organ tissue and cause severe organ damage.
  • The organ damage leads to organ failure, which leads to death.
  • Typical mast cell mediator symptoms and complications like anaphylaxis are less common than in less serious types of SM.
  • The lifespan for MCL is much shorter than normal.
  • Lifespan for MCL is usually quoted as being in the range of 6-18 months. However, there are more recent reports of some patients living 4+ years.
  • In mast cell leukemia, patients die from the organ damage caused by large amounts of mast cells entering and breaking up organ tissue.
  • Fatal anaphylaxis is always a risk with mast cell disease.
  • Of note, there is a newly described chronic form of mast cell leukemia. In this form, patients have stable mast cell disease despite having an overwhelming amount of mast cells in their bodies. The reason for this is unclear and long term survival is not yet known.

Systemic mastocytosis with associated hematologic disease

  • A form of SM in which the patient also has a separate blood disorder that produces too many cells of a different kind.
  • A patient with systemic mastocytosis with associated hematologic disease has too many mast cells and too many blood cells of a different kind. 
  • Previously called SM-AHNMD, systemic mastocytosis with associated clonal hematologic non mast cell lineage disease.
  • The two blood disorders, SM and the other disorder, are treated separately the same way they would be if the patient only had one or the other.
  • The lifespan for SM-AHD is wildly variable as it depends both on which type of SM the patient has as well as the type and severity of the other blood disorder.
  • An important thing to remember is if a patient has SM and another blood disorder that produces too many cells, they are classified as SM-AHD regardless of the type of SM they have. For example, if a patient who has ISM (normal lifespan) also has chronic myelogenous leukemia, they have SM-AHD. However, if the patient has ASM (shortened lifespan) and chronicle myelogenous leukemia, they still have SM-AHD even though the prognosis changes considerably.
  • In SM-AHD, patients die from having an aggressive form of SM, such as MCL or ASM, or as a result of their other blood disorder.
  • Fatal anaphylaxis is always a risk with mast cell disease.

For more detailed reading, please visit these posts:
The Provider Primer Series: Diagnosis and natural history of systemic mastocytosis (ISM, SSM, ASM)
The Provider Primer Series: Diagnosis and natural history of systemic mastocytosis (SM-AHD, MCL, MCS)