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Updated on July 14, 2025
Targeted therapy is a category of cancer treatments that are able to attack specific molecules, or “targets,” found in or on cancer cells. Different targeted therapies work in different ways. Some block cancer cells from using hormones that the cancer needs to grow. Some interrupt the cancer cells’ ability to grow and divide. Some kill cancer cells directly. Targeted therapies are a type of precision medicine, a branch of cancer care that uses specific information about the cancer to plan treatment.
Targeted therapy is a new and emerging approach to treating systemic mastocytosis (SM) and indolent systemic mastocytosis (ISM). The first targeted therapy for SM became available in 2021. In 2023, a dosage of this targeted therapy was approved by the U.S. Food & Drug Administration (FDA) for the treatment of ISM.
Additional targeted therapies are under development for ISM and a more severe type of SM called smoldering systemic mastocytosis (SSM).
SM and ISM
Mast cells are a type of white blood cell that help the body fight infections. When a person has SM, the body produces abnormal mast cells that multiply at a much faster rate and are also more active than normal mast cells. These abnormal mast cells can build up in tissues and organs throughout the body. As these abnormal mast cells activate, they release histamines, which cause an allergic response that can affect many parts of the body—the skin, GI tract, organs like the liver and spleen, the bones, and the blood.
ISM is the most common and also the mildest form of SM. However, it can progress to more advanced forms, and it also puts a person at risk for anaphylaxis, a life-threatening allergic reaction. It’s recommended that a person with any form of SM carry two epinephrine injectors in case of anaphylaxis.
ISM and SM affect different people in different ways, and treatment will be individualized, or tailored to a person’s individual needs:
- Avoiding triggers that cause symptoms to worsen is an important part of treatment, as is using emollients that help make the skin less prone to reacting from triggers.
- Treatment often includes antihistamine medications, drugs called mast cell stabilizers, and therapies that address specific symptoms (such as skin symptoms and GI symptoms).
- A treatment plan can include therapies to address health problems caused by ISM, such as osteoporosis, anemia, and/or low platelet counts.
- Chemotherapy, stem cell transplants, and surgery to remove an enlarged spleen may be treatment options for advanced forms of the condition.
TKI inhibitors
The available targeted therapy and the targeted therapies under development for treating SM and ISM are drugs called tyrosine kinase inhibitors (TKIs). These drugs block the activity of enzymes called tyrosine kinases which play a crucial role in the growth and division of cells. People with SM have gene mutations that lead to the production of abnormal mast cells. TKIs work by disrupting the process affected by this gene mutation, which can reduce the number of mast cells in the body.
BTK inhibitors
Though no drugs in this category are currently available for the treatment of ISM or SM, it’s also worth mentioning Bruton’s tyrosine kinase (BTK) inhibitors. BTK is an enzyme that activates white blood cells, including B cells and mast cells. BTK inhibitors are drugs that block the activity of BTK and have become a mainstay of treatment for certain types of leukemia and lymphoma.
BTK plays a role in the activation of mast cells. BTK inhibitors would not reduce the number of mast cells for a person with SM, but BTK inhibitors can stop mast cells from releasing histamines, which would help reduce symptoms of ISM. Research is ongoing.
Your best source of information
If you or a loved one is living with ISM or another form of SM, your best source of information about treatment options will be your healthcare provider.
