Malignant Mast Cell Neoplasm

Malignant mast cell neoplasms are a group of serious diseases where abnormal mast cells—immune cells that normally help fight infections and control allergic responses—grow out of control and can invade various parts of the body.

Table of contents

• What Are Mast Cells and Their Role
• Types of Malignant Mast Cell Neoplasms
• Identification Codes
• Other Names for This Disease
• Symptoms and Signs
• How the Disease Is Diagnosed
• Who Can Be Affected
• Treatment Options

What Are Mast Cells and Their Role

Mast cells are a type of white blood cell that plays an important role in your immune system^[1]. These cells are normally found in tissues that connect with the outside world, such as the skin, respiratory tract, and intestinal tract. They contain small granules packed with powerful chemicals, including histamine (a substance that causes allergic reactions)^[1].

Under normal circumstances, mast cells help your body fight parasites and participate in allergic reactions. When these cells detect a threat, they release their chemical contents to defend the body. However, when mast cells become abnormal and multiply uncontrollably, they can form tumors or spread throughout the body, causing serious health problems^[2].

Types of Malignant Mast Cell Neoplasms

Malignant mast cell diseases include several different forms, ranging from less aggressive to highly aggressive variants^[1].

Mast cell sarcoma is an extremely rare and aggressive form of the disease. It appears as a single mass that grows destructively in one location^[2][6]. The most common sites where this tumor develops include the voice box, large bowel, the membranes covering the brain, bone, and skin^[6]. Although the disease initially appears in one spot, it can spread to distant parts of the body after several months and may eventually progress to mast cell leukemia^[6].

The cells in mast cell sarcoma are medium to large in size and often have an unusual appearance with bizarre shapes, including cells with multiple nuclei. These cells look quite different from normal mast cells, which can make diagnosis challenging^[2]. In fact, none of the three cases reported in one medical study were correctly identified as mast cell tumors during the first examination^[2].

Mast cell leukemia is another very rare and aggressive variant. About 15% of patients with malignant mast cell disease develop this form^[1]. In this condition, abnormal mast cells are found in large numbers in the bone marrow (20% or more) and also circulate in the bloodstream^[1]. Patients typically experience rapidly worsening organ damage affecting the liver, bone marrow, and other organs. Most patients with mast cell leukemia survive less than one year and respond poorly to treatment^[1].

Systemic mastocytosis is a broader category that includes different types of mast cell disease. In this condition, increased numbers of mast cells are found in organs beyond just the skin, whether or not there are also clusters of mast cells visible on the skin^[1].

Identification Codes

C96.2; C96.22; C96.20
9740/3

Other Names for This Disease

Malignant mast cell tumor, Malignant mastocytoma

Symptoms and Signs

Malignant mast cell neoplasms can cause a wide range of symptoms because mast cells release powerful chemicals that affect many parts of the body^[1]. The symptoms depend on which organs are involved and how much chemical mediators the abnormal mast cells release.

When mast cell tumors appear on the skin, they may look very different from case to case. Some appear as raised bumps on or just below the skin surface, while others look red, ulcerated, bleeding, bruised, or swollen. Some skin tumors stay the same size for months or years, while others grow rapidly over days or weeks. A distinctive feature is that these tumors can increase and decrease in size over time^[5].

Common symptoms related to the release of mast cell chemicals include abdominal pain, episodes of flushing (sudden redness and warmth of the skin), itching, vomiting, diarrhea, bloody stool, lethargy, and decreased appetite^[5]. Many patients experience multiple symptoms affecting different body systems at the same time^[1].

In severe cases, the massive release of chemicals from mast cells can lead to anaphylaxis—a life-threatening allergic reaction that can cause cardiovascular collapse and death if not treated immediately^[1]. Some patients may experience scratching or biting at a mass on their skin, which causes the tumor cells to release more chemicals, leading to localized reactions^[5].

Blood tests may show elevated levels of several substances, including serum tryptase (a specific indicator of mast cell activation), histamine and its breakdown products, heparin, and prostaglandin D2^[1].

How the Disease Is Diagnosed

Diagnosing malignant mast cell neoplasms requires several steps and specialized testing^[2][5].

If a lump or mass is present, doctors often start with a fine needle aspirate. This involves using a small needle to draw out a few cells from the growth. The cells are then examined under a microscope, often by a specialist called a clinical pathologist. Mast cell tumors are usually relatively easy to recognize using this technique^[5].

However, because abnormal mast cells in aggressive tumors can look very different from normal mast cells, special staining techniques are essential for accurate diagnosis. Tissue samples must be tested using immunohistochemical markers—specific antibodies that detect proteins unique to mast cells. The most important markers are antibodies against tryptase and a protein called CD117 (also known as KIT)^[6]. In tissue sections, mast cell disease can be identified by characteristic positive staining for tryptase, along with positive CD68 and negative CD20^[1].

To fully evaluate the disease and determine how aggressive it is, doctors may perform a biopsy or complete surgical removal of the mass. A specialized doctor called a pathologist examines the tissue and assigns a grade that helps predict how the disease will progress^[6].

Additional diagnostic tests may include sampling of nearby lymph nodes, abdominal ultrasound (possibly with samples taken from the liver and spleen), and bone marrow examination^[5][6]. Genetic testing to look for specific mutations in genes, particularly the KIT gene, is also important for diagnosis and treatment planning^[6].

A complete health evaluation includes a thorough physical examination, blood work, and urine analysis. Some patients may need imaging tests such as CT scans or ultrasound to visualize internal masses^[5].

Who Can Be Affected

Malignant mast cell neoplasms are rare diseases that can affect people of different ages. Mast cell sarcoma can appear in a broad range of age groups and in various locations throughout the body^[2].

Interestingly, mast cell sarcoma has occasionally been reported in patients who had a history of infantile cutaneous mastocytosis (a skin condition involving mast cells that appeared in infancy)^[2][5]. This suggests that in some cases, there may be a connection between earlier, less serious forms of mast cell disease and the later development of aggressive tumors.

Mast cell tumors are slightly more common in females^[4]. The average age when the disease is diagnosed varies depending on the specific type of mast cell neoplasm^[4].

Treatment Options

Treatment for malignant mast cell neoplasms depends on the type, location, and extent of the disease^[6].

Surgical removal is the primary treatment recommended for most mast cell tumors. However, these tumors can be challenging to remove completely because what appears to be the visible edge of the tumor is rarely the actual boundary. The tumor often has invisible extensions reaching into surrounding tissue, similar to an octopus with hidden tentacles. Because of this, surgeons must remove tissue well beyond what they can see^[5][6].

Chemotherapy (medications that kill cancer cells) may be used, particularly for aggressive forms of the disease^[6]. Radiation therapy (using high-energy rays to destroy cancer cells) is another treatment option that may be recommended in certain cases^[6].

An important discovery in recent years involves genetic testing of mast cell sarcomas. Studies have found that most cases of mast cell sarcoma do not have a specific mutation called KIT D816V, which is common in other forms of mast cell disease. This is significant because the KIT D816V mutation makes tumors resistant to a targeted therapy drug called imatinib. Mast cell sarcomas without this mutation may respond to imatinib or similar targeted therapies^[2][5]. This means that accurate diagnosis of mast cell sarcoma could allow patients to receive specific targeted treatment that might be effective for this aggressive disease.

The outlook for patients with malignant mast cell neoplasms varies considerably depending on the specific type of disease. Mast cell leukemia has a very poor prognosis, with most patients surviving less than one year^[1]. Mast cell sarcoma typically progresses rapidly, with distant spread occurring after several months and potential progression to a terminal phase resembling mast cell leukemia^[6].