What percentage of Diffuse Large B-Cell Lymphoma (DLBCL) cases are FMC7 positive?

FMC7 Positivity in Diffuse Large B-Cell Lymphoma (DLBCL)

In Diffuse Large B-Cell Lymphoma (DLBCL), FMC7 positivity is present in over 90% of cases, based on the most recent immunophenotypic data.

Immunophenotypic Profile of DLBCL

DLBCL has a characteristic immunophenotypic profile that helps distinguish it from other lymphomas. The typical immunophenotype includes:

• Consistently positive markers (>90% of cases):

  • CD19
  • CD20
  • CD22
  • CD38
  • CD45
  • CD79a
  • HLA-DR
  • FMC7 1

• Variable expression markers:

  • CD5 (positive in some cases, but more commonly associated with mantle cell lymphoma)
  • CD10 (positive in germinal center B-cell like subtype)
  • BCL6 (commonly expressed in germinal center B-cell like subtype)

Diagnostic Implications

The high rate of FMC7 positivity in DLBCL has important diagnostic implications:

• FMC7 positivity helps differentiate DLBCL from certain other lymphomas, particularly when used as part of a comprehensive immunophenotyping panel
• When evaluating a suspected DLBCL case, immunophenotyping should include a panel of markers including FMC7 2

Clinical Context

Understanding the immunophenotypic profile of DLBCL is crucial for:

1. Accurate diagnosis: A comprehensive immunohistochemical panel including FMC7 is essential for confirming DLBCL diagnosis 2

2. Distinguishing variant forms: Proper immunophenotyping helps identify variant forms such as immunoblastic lymphoma, primary mediastinal B-cell lymphoma, T-cell/histiocyte rich large B-cell lymphoma, and other subtypes 2

3. Differentiating from other diagnoses: The immunophenotypic profile helps distinguish DLBCL from other entities that may appear morphologically similar but have different clinical implications 2

Diagnostic Approach

For optimal diagnosis of DLBCL:

• Surgical excision biopsy is the preferred method of diagnosis 2
• Fresh, unfixed tissue should be sent to the laboratory to allow for flow cytometric studies 2
• Immunophenotypic investigations should be performed using either immunohistochemistry, flow cytometry, or both 2
• A comprehensive panel including CD20, CD79a, BCL6, CD10, MYC, BCL2, Ki67, IRF4, CyclinD1, CD5, CD23, and FMC7 is recommended 2

Comparison with Other Lymphomas

While FMC7 is positive in >90% of DLBCL cases, its expression pattern differs in other B-cell lymphomas:

• Mantle Cell Lymphoma: Also typically shows FMC7 positivity (>90%) along with CD5 positivity and CD23 negativity 2
• Chronic Lymphocytic Leukemia: Usually FMC7 negative, CD5 positive, and CD23 positive
• Follicular Lymphoma: Variable FMC7 expression, typically CD10 positive

Clinical Significance

The high rate of FMC7 positivity in DLBCL has practical implications:

• It serves as a useful diagnostic marker when included in flow cytometry panels
• It can help identify DLBCL cells in blood or cerebrospinal fluid samples during staging or monitoring for disease progression 2
• In cases with leukemic presentation of DLBCL, FMC7 positivity is observed in >90% of cases, helping to confirm the diagnosis 1

Understanding the immunophenotypic profile, including FMC7 positivity, is essential for accurate diagnosis and appropriate management of patients with DLBCL.