Mast cell tumor pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Pathophysiology

Mast Cell

• A mast cell originates from the bone marrow and is normally found throughout the connective tissue of the body.
• It is a normal component of the immune system and as it releases histamine it is associated with allergic reactions.
• Mast cell granules contain histamine, heparin, platelet-activating factor, and other substances.
• It is thought that the effects of mast cell tumor relate at least in part to mediator release.
• In systemic mastocytosis, abnormal proliferation and microscopic infiltration of mast cells involves skin, bone marrow, gastrointestinal tract, liver, and spleen.

Genetics

• Mast cells express a cell surface receptor, ''C-Kit'' (CD117), which is the receptor for stem cell factor. In laboratory studies, stem cell factor appears to be important for the proliferation of mast cells.
• Mutations of the C-KIT receptor, leading to uncontrolled stimulation of the receptor, is a cause for the disease.
• The D816V point mutation within the tyrosine kinase Kit (C-Kit) that is detected in 80% of cases is considered a driver mutation causing the permanent receptor activation and consequent proliferation, and thus neoplastic expansion of the mutated mast cell clone.
• The following genes are involved in the pathogenesis of mast cell tumor:

• KIT
• RAS
• JAK2
• TET2
• DNMT3A
• ASXL1
• CBI

Microscopic Pathology

• Cells in the superficial/mid dermis that are:

• Lymphocyte-like with more cytoplasm that is granular
• Cells may have spindled or stellate morphology

• Tend to be more abundant around vessels
• Eosinophils may present

• 

  Micrograph showing a mast cell tumor.