Mast cell leukemia (MCL) is generally considered the most severe subtype of systemic mastocytosis (SM). MCL is a form of blood cancer. It is both very rare and extremely aggressive, making it a challenge to treat.
What characterizes mast cell leukemia?
MCL is seen in less than 5% of all cases of SM. It is characterized by the uncontrolled expansion of primarily immature mast cells, both in the bone marrow where they originate and in other organs in the body.
Mast cells are immune cells that release histamine and other chemicals in response to allergens or injury. While these cells are necessary for the body to defend itself, in MCL they accumulate and grow in an excessive, uncontrolled manner. This often results in significant organ damage.
Physicians diagnose SM and determine its subtype via specific criteria set by the World Health Organization. These criteria depend on specific laboratory findings from various tests, such as a bone marrow biopsy. In addition to the set criteria for SM, to be diagnosed with MCL patients must also have at least 20% atypical mast cells in the bone marrow or 10% in the blood.
Read more about SM testing and diagnosis
What is the clinical course and prognosis of MCL?
Given that MCL is a rare subtype of an already rare disease, there is much about it that is still poorly understood. Hence, much that is known about this disease comes from case reports, as opposed to clinical studies that recruit real-life patients.
Generally, MCL can be acute or chronic. In acute MCL, the disease progresses very quickly and aggressively. Significant organ damage can occur very rapidly. This form of MCL is seen in the vast majority of patients (up to nine in 10 individuals).
In chronic MCL, the disease unfolds more slowly over a prolonged period of time. As such, there is typically no evidence of rapid organ damage. However, at some point, chronic MCL usually progresses to acute MCL.
The prognosis of MCL is generally regarded to be the poorest among the subtypes of SM. One study found the median overall survival of patients with MCL was approximately 1.6 years. Prognosis varies according to factors such as the aggressiveness of the disease and how a patient responds to treatment.
How is mast cell leukemia treated?
MCL is typically managed by both hematology and oncology teams, and treatment is highly tailored towards the individual patient.
An aspect of MCL treatment is the reduction of SM-related symptoms. This may include a treatment strategy of antihistamines for relieving itching and corticosteroids for alleviating inflammation.
Another aspect of treatment is to slow the proliferation of mast cells. The uncontrolled proliferation of mast cells is the defining feature of this blood cancer. Therapies such as tyrosine kinase inhibitors may be prescribed to inhibit cell proliferation and survival.
Chemotherapy is often needed to reduce the number of malignant mast cells. One of the most common chemotherapies used to treat MCL is cladribine.
Some patients with MCL may be eligible for stem cell transplantation. However, this procedure carries significant risks and is only offered to patients in whom the potential benefits outweigh the potential risks.
With any treatment plan, doctors will closely monitor how patients respond to initial therapies and then adjust treatment accordingly. The main goal of treatment in MCL is to reduce the symptoms associated with this disease and to prolong life expectancy.
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