Ideal Sample for Flow Cytometry to Detect Splenic Marginal Zone Lymphoma (SMZL)
For SMZL detection, peripheral blood with flow cytometry is the ideal first-line sample, with bone marrow aspirate and biopsy reserved for cases where diagnosis remains uncertain. 1 Flow cytometry of peripheral blood is considered mandatory in the diagnostic workup of SMZL according to European Society for Medical Oncology (ESMO) guidelines.
Diagnostic Approach for SMZL
First-Line Samples:
- Peripheral blood with flow cytometry (mandatory)
- Allows detection of characteristic immunophenotype
- Can identify villous lymphocytes (though not seen in all cases)
- Less invasive than other sampling methods
Second-Line Samples (if diagnosis remains uncertain):
- Bone marrow aspirate with flow cytometry
- Bone marrow biopsy with histology and immunohistochemistry
- Look for intrasinusoidal infiltration pattern by CD20+ cells
- Evaluate for characteristic immunophenotype
Last Resort (only if diagnosis remains uncertain):
- Splenectomy specimen
- Historically considered the gold standard
- Now reserved only for cases where diagnosis cannot be established through less invasive methods 1
- Provides definitive diagnosis through visualization of characteristic micronodular infiltration with marginal zone differentiation
Immunophenotyping Profile to Look For
Positive Markers:
- CD19, CD20, CD22, CD79a
- Surface immunoglobulin (usually IgM±IgD)
Negative Markers:
- CD5 (negative in most cases, though can be positive in ~30%)
- CD10, CD23, CD43, cyclin D1
Variable Expression:
- CD103, CD11c, CD25 1
Diagnostic Accuracy Considerations
- Concordance between bone marrow histology and flow cytometry is found in 87% of cases 2
- Most discordant cases have positive histology but negative flow cytometry, suggesting histology may be more sensitive 2
- Peripheral blood flow cytometry combined with bone marrow examination can establish diagnosis in most cases, avoiding splenectomy 1
Common Pitfalls and Caveats
Villous lymphocytes are not pathognomonic:
- Not seen in all SMZL cases (sometimes due to technical reasons)
- Not every lymphoma with villous lymphocytes is SMZL 3
Differential diagnosis challenges:
- Must differentiate from splenic diffuse red pulp lymphoma, hairy cell leukemia variant, lymphoplasmacytic lymphoma, CLL, and mantle cell lymphoma
- Bone marrow histopathology alone cannot reliably distinguish SMZL from splenic diffuse red pulp small B-cell lymphoma 4
Molecular testing importance:
- Test for NOTCH2 mutations (present in 10-25% of SMZL cases)
- MYD88 mutation should be negative (helps distinguish from lymphoplasmacytic lymphoma)
- FISH studies for deletion of 7q can serve as diagnostic biomarker 1
By following this approach, most cases of SMZL can be diagnosed without resorting to splenectomy, which should be avoided when possible due to associated morbidity.