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Mastocytosis

For medical students2 min readUpdated 2026-10-10

Mastocytosis is a rare heterogeneous condition characterized by a pathological increase in the number of mast cells in body tissues. The process can involve the skin, bone marrow, liver, spleen, and the gastrointestinal tract.

Genetic mutationPoint mutation at codon 816 of the C-Kit gene

ImmunophenotypeCo-expression of CD2 and/or CD25 markers

Laboratory markerElevated total serum tryptase levels

Primary cell typeDrastic expansion of the mast cell population

Diagnostic Markers

To confirm the diagnosis, clinicians utilize a combination of laboratory, immunological, and cytogenetic criteria:

Cytogenetics: Detection of the characteristic point mutation at codon 816 of the C-Kit gene, which encodes the CD117-Kit stem cell factor receptor.
Immunophenotype: Identification of the co-expression of cell surface markers CD2 and/or CD25.
Laboratory parameters: A significant increase in serum total tryptase levels.

Classification of Mast Cell Neoplasms

According to the World Health Organization (WHO) classification, the pathology is divided into several main forms and variants:

Cutaneous mastocytosis — the pathological process is localized predominantly in the skin.
Indolent systemic mastocytosis — may present with or without skin involvement, with bone marrow infiltration of less than 30%.
Systemic mastocytosis with an associated clonal hematologic non-mast cell lineage disease (AHN) — may also involve the skin.
Aggressive systemic mastocytosis — characterized by multiorgan infiltration, clonal proliferation of atypical mast cells, and less than 20% immature forms in the bone marrow.
Mast cell leukemia/sarcoma — a severe form characterized by the presence of more than 20% immature mast cells in the bone marrow.

Localization of the Pathological Process

The expansion of mast cells in this condition is not limited to a single anatomical zone. Pathological infiltration may encompass:

Skin
Bone marrow
Liver and spleen tissues
Gastrointestinal tract
Other organs in systemic and aggressive forms of the disease

Mnemonic

C-Kit cells elevate tryptase in the skin and bone marrow.

Frequently asked questions

Which clonal hematologic disorders are most commonly associated with systemic mastocytosis?

Systemic mastocytosis can be associated with hematological neoplasms. Associated conditions include:

Myelodysplastic syndromes (MDS).
Myeloproliferative neoplasms.
Leukemias.
Lymphomas.

The WHO classification distinguishes a specific subcategory: systemic mastocytosis with an associated hematological neoplasm (SM-AHN).

What changes occur in the body during mastocytosis?

The primary manifestation of the disease is a significant increase in the number of mast cells across various body tissues, including the skin, bone marrow, spleen, liver, and gastrointestinal tract.

What genetic defect is characteristic of this condition?

The primary cytogenetic marker is a point mutation at codon 816 of the C-Kit gene, which encodes the CD117-Kit growth factor receptor.

How are forms with bone marrow involvement classified based on the degree of infiltration?

In the indolent form, infiltration is less than 30%; in the aggressive form, there are less than 20% immature mast cells with signs of clonal proliferation; and in mast cell leukemia, immature forms exceed 20%.

Go deeper

WHO diagnostic criteria for systemic mastocytosis
Clinical manifestations of cutaneous mastocytosis
Differential diagnosis of aggressive forms and leukemia
The role of tryptase in symptom pathogenesis
Morphological findings in bone marrow biopsies