Systemic mastocytosis is a rare blood disorder where abnormal mast cells—a type of white blood cell—accumulate in various organs throughout the body. These cells, meant to protect us from threats, instead multiply uncontrollably and release substances that trigger allergic-like symptoms affecting the skin, digestive system, bones, and other organs. While there is no cure, modern therapies aim to control symptoms, prevent complications, and improve quality of life for those living with this challenging condition.

When Immune Cells Turn Against the Body

Managing systemic mastocytosis involves addressing two fundamental problems: reducing the symptoms caused by chemicals released from abnormal mast cells and, in more severe cases, controlling the excessive buildup of these cells in vital organs. The treatment approach depends greatly on which type of systemic mastocytosis a person has, as well as how severely symptoms affect daily life and overall health.^[1][2]

Healthcare providers typically classify systemic mastocytosis into different subtypes ranging from mild to severe. Indolent systemic mastocytosis, the most common form, usually causes manageable symptoms that develop gradually over years. More aggressive forms involve organ damage and may progress more rapidly. Because each person experiences the condition differently, treatment plans must be highly individualized, taking into account not just the disease subtype but also specific symptom patterns and overall health status.^[9][14]

Medical societies have developed clinical guidelines to help doctors choose appropriate therapies. These guidelines recognize that standard treatments approved for long-term use form the backbone of care for most patients, while ongoing research into new medications offers hope for those with more challenging cases. Clinical trials testing innovative therapies continue to expand treatment options, particularly for advanced forms of the disease where traditional approaches may not provide adequate control.^[4][15]

Standard Approaches to Symptom Control

The foundation of treatment for most people with systemic mastocytosis focuses on preventing mast cells from releasing their troublesome chemicals and blocking the effects of substances that do get released. Antihistamines represent the first line of defense. These medications work by blocking histamine, the primary chemical responsible for many symptoms including itching, flushing, and hives. Doctors often prescribe both H1 antihistamines (which mainly affect the skin) and H2 antihistamines (which particularly help with stomach symptoms). Some patients take non-sedating antihistamines during the day and sedating ones at bedtime to ensure round-the-clock symptom control.^[7][11][13]

When skin symptoms persist despite antihistamines, doctors may add a very strong steroid cream applied directly to affected areas. This treatment reduces the number of mast cells in the skin that can release histamine and trigger inflammation. However, steroid creams must be used carefully and for limited periods because prolonged use can thin the skin, cause stretch marks, or lead to easy bruising. Patients should apply the cream only to lesions rather than large areas of normal skin to minimize these risks.^[11]

For digestive problems like stomach pain, diarrhea, and heartburn, several medication options exist. H2-receptor antagonists help by blocking histamine’s effects in the stomach, which normally stimulates acid production that can damage the stomach lining. Many doctors now prefer proton pump inhibitors, which more powerfully reduce stomach acid. A medication called sodium cromoglicate (also known as cromolyn sodium) acts as a mast cell stabilizer, meaning it prevents mast cells from releasing their chemicals in the first place. This can be particularly helpful for abdominal pain and diarrhea, though it may not work well for all patients since it isn’t absorbed efficiently from the intestines.^[11][13][15]

When bone involvement causes osteoporosis or bone pain, bisphosphonates become important. These medications slow down bone breakdown while allowing new bone formation to continue, which improves bone density and strength. Patients may also receive calcium supplements since calcium is essential for bone health. Bone pain that doesn’t respond to other treatments might require short courses of oral corticosteroids, though doctors try to limit steroid use because long-term treatment can cause weight gain, mood changes, fluid retention, and other side effects.^[11][13]

Leukotriene antagonists such as zafirlukast and montelukast, medications typically used for asthma, sometimes help systemic mastocytosis patients. These drugs block the effects of leukotrienes, another group of chemicals released by mast cells. For severe itching that doesn’t respond to other treatments, doctors may try psoralen plus ultraviolet A therapy (PUVA). This involves taking a medication called psoralen that makes skin more sensitive to light, followed by controlled exposure to ultraviolet A wavelengths. The treatment can temporarily relieve itching and fade skin lesions, though patients can only receive a limited number of sessions over their lifetime due to long-term skin cancer risk.^[11][13]

An emerging option for patients with recurrent anaphylaxis despite optimal preventive therapy is omalizumab, a medication that blocks immunoglobulin E (IgE) from attaching to mast cells. Some patients have experienced reduced frequency of anaphylaxis episodes with this treatment, though it’s not approved specifically for mastocytosis and is considered “off-label” use. Patients still need to carry epinephrine even while taking omalizumab. The duration of standard treatments varies widely—some medications may be needed for a few weeks to address acute symptoms, while others continue indefinitely to maintain symptom control.^[13][15]

Advanced Therapies for Aggressive Disease

When systemic mastocytosis causes organ damage or when symptoms cannot be controlled with standard medications, doctors consider cytoreductive treatments—therapies designed to reduce the number of abnormal mast cells throughout the body. These approaches are particularly important for aggressive systemic mastocytosis, systemic mastocytosis with an associated blood disorder, and mast cell leukemia.^[9][15]

The breakthrough in treating systemic mastocytosis came with understanding that most cases involve a specific genetic mutation called KIT D816V. This mutation occurs in approximately 95% of patients and causes a protein receptor to stay permanently “switched on,” leading to uncontrolled mast cell growth and activation. Recognizing this mechanism opened the door to developing targeted therapies that specifically block this abnormal signaling.^[3][5][6]

Interferon alpha, originally developed to treat cancer, has shown effectiveness in some cases of aggressive mastocytosis. While researchers don’t fully understand why it works, the medication appears to reduce mast cell production in the bone marrow. Patients receive interferon alpha by injection. When starting treatment, many people experience flu-like symptoms including chills, fever, and joint pain, though these effects typically improve as the body adjusts to the medication.^[11][13]

Innovative Treatments in Clinical Research

Clinical trials testing new medications represent a crucial frontier in systemic mastocytosis treatment, particularly for patients with advanced forms of the disease where conventional options provide limited benefit. Understanding what phase a trial is in helps patients and doctors evaluate potential treatments. Phase I trials primarily assess safety and determine appropriate dosing in small groups of patients. Phase II trials expand to larger groups to evaluate whether the treatment actually works and continues to be safe. Phase III trials compare the new treatment directly against current standard therapies in large patient populations to determine if the new option offers superior results.^[15]

The development of tyrosine kinase inhibitors specifically targeting the KIT mutation has transformed care for advanced systemic mastocytosis. Imatinib mesylate was the first drug approved for treating systemic mastocytosis, but it only works for the small percentage of patients who don’t have the KIT D816V mutation or who have wild-type (normal) KIT. Unfortunately, this medication is ineffective against the D816V mutation that most patients carry. Other tyrosine kinase inhibitors like dasatinib and nilotinib also proved ineffective for typical mastocytosis patients.^[11][13][15]

Midostaurin represented a major advancement because it can inhibit both wild-type KIT and the mutant KIT D816V receptor. This medication received approval for treating advanced systemic mastocytosis based on clinical trials showing it could reduce mast cell burden and improve symptoms in patients with aggressive disease. Midostaurin works by blocking multiple kinases involved in cell growth and survival pathways. Clinical trial data demonstrated that patients treated with midostaurin experienced improvements in organ function, reduced symptom burden, and better quality of life compared to baseline. The medication is taken orally twice daily, and common side effects include nausea, vomiting, diarrhea, and low blood cell counts that require monitoring.^[13][15]

A newer agent called avapritinib is a highly selective inhibitor designed specifically to target the KIT D816V mutation. Because it’s more selective for the mutant receptor, researchers hoped it might cause fewer side effects than less selective inhibitors. Clinical trials of avapritinib in advanced systemic mastocytosis have shown promising results, with patients experiencing significant reductions in mast cell burden and improvements in symptoms. The medication received approval for treating advanced systemic mastocytosis. Avapritinib is taken once daily as an oral tablet. Side effects seen in trials included cognitive effects (such as problems with memory or attention), swelling, changes in hair color, gastrointestinal symptoms, and low blood cell counts.^[15]

Cladribine, a type of medication called a purine analog, offers another approach. Originally developed for other blood disorders, cladribine shows significant activity against certain white blood cells. Scientists believe it may work in mastocytosis because mast cells might share a common ancestor cell with monocytes, which cladribine effectively targets. Clinical experience with cladribine has shown variable but sometimes substantial responses in advanced systemic mastocytosis patients. The medication is given as an intravenous infusion over several days, typically for one or more cycles. Duration of response varies among patients, with some experiencing prolonged benefit while others eventually need additional treatment.^[15]

For the most severe cases of aggressive systemic mastocytosis or mast cell leukemia, particularly in younger patients with good overall health, doctors may consider allogeneic stem cell transplantation. This intensive procedure involves replacing the patient’s bone marrow with healthy stem cells from a donor after high-dose chemotherapy destroys the abnormal mast cells. While potentially offering the only curative option for advanced disease, stem cell transplantation carries significant risks including graft rejection, graft-versus-host disease (where donor cells attack the patient’s body), infections, and treatment-related complications. The decision to proceed requires careful evaluation by a multidisciplinary team and extensive discussion with patients about potential benefits versus risks.^[15]

Ongoing research continues exploring additional mechanisms that might be targeted in systemic mastocytosis. Scientists are investigating how mast cells interact with their surrounding environment, studying additional genetic changes beyond KIT mutations that might contribute to disease behavior, and developing therapies that could prevent organ damage even when mast cell numbers remain elevated. Combination approaches using multiple agents simultaneously are also under investigation, with the goal of achieving more complete and durable responses than single agents provide.^[15]

Most common treatment methods

• Antihistamine therapy
  • H1 antihistamines to control itching, flushing, and hives affecting the skin
  • H2 antihistamines to reduce stomach acid and help with gastrointestinal symptoms
  • Non-sedating antihistamines for daytime use and sedating ones for nighttime
  • Forms the primary treatment approach for mild to moderate symptoms
• Mast cell stabilizers
  • Sodium cromoglicate (cromolyn sodium) prevents mast cells from releasing chemicals
  • Particularly helpful for abdominal pain, diarrhea, and gastrointestinal symptoms
  • May improve cognitive symptoms in some patients
• Corticosteroid treatments
  • Topical steroid creams for skin lesions when antihistamines aren’t sufficient
  • Short courses of oral steroids for severe symptoms or bone pain
  • Used to control malabsorption and prevent anaphylaxis in selected cases
  • Limited long-term use due to potential side effects
• Bone-protective medications
  • Bisphosphonates to slow bone breakdown and improve bone density
  • Calcium supplements to support bone health
  • Treatment for osteoporosis caused by mast cell accumulation in bones
• Tyrosine kinase inhibitors
  • Imatinib for patients without the KIT D816V mutation
  • Midostaurin for advanced systemic mastocytosis with activity against KIT D816V
  • Avapritinib as a selective KIT D816V inhibitor for advanced disease
  • Taken orally with regular monitoring for side effects and blood counts
• Cytoreductive agents
  • Interferon alpha to reduce mast cell production in bone marrow
  • Cladribine, a purine analog showing activity in advanced cases
  • Reserved for patients with organ damage or inadequate symptom control
• Emergency interventions
  • Epinephrine auto-injectors for treating severe allergic reactions and anaphylaxis
  • All patients should carry and know how to use emergency epinephrine
  • Training for family members in recognizing and responding to anaphylaxis