Updated on December 29, 2025
Indolent systemic mastocytosis (ISM) is a mild but persistent form of systemic mastocytosis. Systemic mastocytosis is a group of cancers characterized by the overgrowth of white blood cells called mast cells. Under normal circumstances, mast cells help the body fight infections and repair injuries.
When a person has a form of systemic mastocytosis, the body produces abnormal mast cells. These abnormal mast cells replicate much more quickly than normal mast cells. They are also more active.
People with ISM can experience a number of symptoms as a result of the increased number and increased activity of mast cells. Common symptoms include skin lesions, skin flushing, fainting and fatigue, headaches, and gastrointestinal problems.
While there is no cure for ISM, the condition can be managed with treatment, and people with the condition typically have a normal or near normal life expectancy.
However, ISM does have serious health risks. It puts a person at risk for life-threatening allergic reactions (anaphylaxis) as a result of the abnormally high number of mast cells in the body. While ISM is considered a mild form of systemic mastocytosis, it can progress to advanced forms. Advanced forms of the disease can cause life-threatening mast cell buildup that damages the bones, bone marrow, liver, spleen, and lymph nodes.
Treatment for ISM
Treatment focuses on controlling symptoms and preventing complications. Avoiding triggers is an essential part of treatment. Triggers are things that cause mast cells to become active—allergens, alcohol, temperature changes, insect bites, and spicy foods are a few examples. Certain medications are also potential triggers (and there will be a bit more on this below).
Medications are also an essential part of a treatment plan for ISM. The medications that a person requires will depend on their symptoms. Examples include:
- Antihistamines and leukotriene modifiers to block chemicals released by active mast cells, used to treat skin symptoms and gastrointestinal symptoms
- Mast cell stabilizers, drugs that stabilize the outer layer of mast cells (the membrane) and prevent mast cells from releasing chemicals
- Proton pump inhibitors, prescribed when ISM causes gastroesophageal reflux (acid reflux)
- Drugs called tyrosine kinase inhibitors (TKIs) which interfere with the growth of abnormal mast cells and help reduce the number of abnormal mast cells
- Epinephrine auto-injectors that need to be carried in case of anaphylaxis
A treatment plan may include multiple medications
The need to adhere to multiple dosing schedules for multiple drugs can be challenging. But better adherence will help you get the most out of treatment. With that in mind, here are some strategies that can help.
Have clear instructions
- Always have clear instructions on how to take each medication. Know when each medication needs to be taken, how it needs to be taken, and any additional instructions (such as taking a medication with or without food).
- Have proper training on how to administer an epinephrine autoinjector.
- If you have questions or concerns, your healthcare provider and pharmacist will be your best sources of information
Know what medications can trigger symptoms
- Medications such as non-steroidal anti-inflammatory drugs (NSAIDs), opioids, local anesthetics, antibiotics, and contrast dyes (used in some imaging tests) can activate mast cells. Ask your provider for a list of medications you will need to avoid.
- Have a list of all medications you are taking, including prescription medications, over the counter medications, and supplements. Each of your healthcare providers should have a copy of this list.
Stay organized
- For oral medications, consider using a pill organizer that arranges pills into individual doses labeled with the days of the week.
- Write down the daily, weekly, and monthly medication schedule in detail. Keep this schedule in a place where it is easy to check.
- Store all medications in the same place and keep that space organized.
Reminders and routines
- Set alarms and reminders on your phone. Some pharmacy apps also allow you to set reminders.
- Have a backup reminder, such as a note or other visual cue left in a place where it will be difficult to miss.
- Make taking medications part of your daily routine, such as brushing your teeth.
- Add all healthcare appointments to your calendar.
Plan for the unexpected
- Have doses of medications ready in case you are not home in time to take a medication.
- Plan ahead if you are going to be traveling. Pack enough medication, have a copy of your dosing schedule, medical information, and emergency contacts.
- Also inform your healthcare provider about travel or anything that could conflict with scheduled appointments.
If you are having difficulty following treatment for any reason, talk about it with your healthcare provider. They are there to help you come up with solutions.
Also ask about newer therapies and emerging therapies. While everyone’s treatment plan is different, some research has found that treating with TKI drugs can help reduce the number of medications some people need to take to manage symptoms.