How to diagnose splenic marginal zone lymphoma (SMZL) with a NOTCH2 mutation?

Diagnosing Splenic Marginal Zone Lymphoma (SMZL) with NOTCH2 Mutation

The diagnosis of SMZL with NOTCH2 mutation requires a combination of peripheral blood/bone marrow evaluation, flow cytometry, immunohistochemistry, and molecular testing for NOTCH2 mutations, with splenectomy being necessary only in a minority of cases. 1

Initial Diagnostic Approach

Clinical and Laboratory Assessment

• Complete history and physical examination, focusing on:
  • Lymph node regions
  • Liver and spleen size
  • Constitutional symptoms
• Laboratory workup:
  • Full blood count with differential
  • Flow cytometry of peripheral blood (mandatory)
  • Biochemistry including renal and liver function tests
  • Protein electrophoresis
  • LDH and β2-microglobulin
  • Direct antiglobulin (Coombs) test
  • Serum and urine immunofixation
  • Viral serology (HCV, HBV, HIV) 1

Imaging Studies

• Complete chest and abdominal CT scan or MRI
• Abdominal sonography (provides additional information for detection of splenic focal lesions)
• PET-CT (consider if high-grade transformation is suspected) 1

Definitive Diagnosis

Bone Marrow Assessment

• Bone marrow aspirate with morphology and flow cytometry
• Bone marrow biopsy with immunohistochemistry
  • Look for intrasinusoidal infiltration by CD20+ cells (characteristic feature) 1, 2

Peripheral Blood Evaluation

• Assess for characteristic villous lymphocytes (though not seen in all cases)
• Immunophenotyping to identify typical SMZL profile 1

Molecular Testing

• NOTCH2 mutation testing is crucial as it:
  • Is present in approximately 20% of SMZL cases
  • Typically affects the PEST domain, causing impaired protein degradation
  • Represents a potential diagnostic biomarker specific to SMZL 3
• Additional molecular markers:
  • MYD88 L265P mutation (present in ~15% of cases)
  • KLF2 mutations
  • 7q deletion (almost specific to SMZL) 2, 4

Splenectomy Considerations

• In most cases, diagnosis can be established without splenectomy
• Splenectomy may be necessary in a minority of cases:
  • When peripheral blood/bone marrow findings are inconclusive
  • For differential diagnosis between SMZL and splenic diffuse red pulp lymphoma 1

Diagnostic Algorithm

1. Initial suspicion: Based on splenomegaly, lymphocytosis, and/or cytopenias
2. First-line tests: Complete blood count, peripheral blood smear, flow cytometry
3. Confirmatory tests:
   • Bone marrow biopsy with immunohistochemistry
   • Molecular testing for NOTCH2 mutations and other genetic markers
4. If inconclusive: Consider splenectomy for definitive diagnosis

Prognostic Implications of NOTCH2 Mutations

• NOTCH2 mutations are associated with:
  • Deregulation of marginal zone B-cell development
  • Potentially more aggressive disease requiring earlier intervention
  • Better response to rituximab plus bendamustine therapy 5, 3

Common Pitfalls and Caveats

• Villous lymphocytes are not seen in all SMZL cases and can be present in other lymphomas
• Differential diagnosis should include:
  • Lymphoplasmacytic lymphoma (check for MYD88 mutations)
  • Splenic diffuse red pulp lymphoma
  • Hairy cell leukemia
• NOTCH2 mutations are almost specific to SMZL among indolent B-cell lymphoproliferative disorders, making them valuable diagnostic markers 3
• Expert hematopathologist review is essential for accurate diagnosis 1

By following this comprehensive diagnostic approach, SMZL with NOTCH2 mutation can be accurately identified, allowing for appropriate risk stratification and treatment selection.