Differential Diagnosis for Mild Increase in Atypical Mast Cells with No CD2 Expression

• Single Most Likely Diagnosis

  • Systemic Mastocytosis: This condition is characterized by an accumulation of mast cells in one or more organs, often presenting with atypical mast cells. The absence of CD2 expression is a common finding in systemic mastocytosis, particularly in the context of the World Health Organization (WHO) criteria, which include the presence of mast cells that express CD25 and/or CD2 negativity in conjunction with other specific mast cell markers.

• Other Likely Diagnoses

  • Mast Cell Leukemia: Although less common, mast cell leukemia can present with atypical mast cells in the blood or bone marrow. The lack of CD2 expression might be seen, but this diagnosis is generally considered when there's a significant increase in mast cells, often with more pronounced cytological atypia.
  • Myeloproliferative Neoplasm (MPN) with Mast Cell Component: Some MPNs can have a mast cell component, and while CD2 expression might not be a defining feature, the presence of atypical mast cells alongside other myeloproliferative features could suggest this diagnosis.

• Do Not Miss Diagnoses

  • Acute Myeloid Leukemia (AML) with Mast Cell Involvement: AML can rarely present with mast cell involvement, and missing this diagnosis could have significant implications for treatment and prognosis. The absence of CD2 on mast cells does not rule out AML, as the leukemic cells themselves may express a variety of markers.
  • Lymphoma with Mast Cell Infiltration: Certain lymphomas can have a significant mast cell component, and while the lymphoma cells would be the primary focus, recognizing the mast cell infiltration is crucial for understanding the tumor microenvironment and potential treatment responses.

• Rare Diagnoses

  • Mast Cell Sarcoma: A rare tumor consisting of mast cells that can present with atypical morphology and variable marker expression, including the absence of CD2. This diagnosis would be considered with a localized mass of mast cells and appropriate clinical context.
  • Monoclonal Mast Cell Activation Syndrome: This is a rare condition characterized by an expansion of mast cell clones without the typical accumulation seen in systemic mastocytosis. The clinical presentation and lack of CD2 expression might suggest this diagnosis in the appropriate context, although it is less well-defined and might require further investigation to confirm.