What is the diagnostic approach for Chronic Lymphocytic Leukemia (CLL)?

Diagnostic Approach for Chronic Lymphocytic Leukemia (CLL)

The diagnosis of CLL is primarily established through immunophenotyping of peripheral blood, which is sufficient in most cases without the need for lymph node or bone marrow biopsy. 1

Essential Diagnostic Criteria

Primary Diagnostic Tests

• Complete Blood Count (CBC)

  • Absolute lymphocyte count ≥5 × 10^9/L persisting for at least 3 months 2
  • Examination of peripheral blood smear showing small, mature lymphocytes with:
    • Narrow border of cytoplasm
    • Dense nucleus lacking discernible nucleoli
    • Partially aggregated chromatin 2
    • Presence of smudge cells (though not pathognomonic) 3

• Flow Cytometry Immunophenotyping (most critical diagnostic test) 2

  • Required characteristic immunophenotype:
    • CD5+ (positive)
    • CD19+ (positive)
    • CD20+ (dim expression)
    • CD23+ (positive)
    • Restricted kappa or lambda light chain expression
    • Surface immunoglobulin (sIg) with weak expression 1, 2

Diagnostic Scoring System

The CLL immunophenotypic scoring system helps confirm diagnosis by evaluating:

• CD5 positivity
• CD23 positivity
• Weak surface immunoglobulin expression
• Dim CD20 expression
• Weak or negative CD79b 1, 2

Differential Diagnosis

Flow cytometry is essential to differentiate CLL from other B-cell disorders:

• Mantle Cell Lymphoma (MCL)

  • Usually CD23 negative
  • For CD23+ cases, additional testing needed:
    • RT-PCR for cyclin D1 overexpression
    • FISH for t(11;14) translocation
    • CD200 expression (positive in CLL, negative in MCL)
    • SOX11 staining on biopsies 1

• Marginal Zone Lymphoma (MZL)

  • Usually CD23 negative
  • Negative or low CD43 expression
  • High CD180 expression 1

• Lymphoplasmacytic Lymphoma

  • May express CD5 but typically CD23 negative 1

Additional Testing When Diagnosis Is Unclear

• Lymph Node Biopsy

  • Indicated when immunophenotyping is not conclusive 1
  • Essential for confirming Small Lymphocytic Lymphoma (SLL) when B lymphocytes in peripheral blood are <5 × 10^9/L with lymphadenopathy/splenomegaly 1

• Bone Marrow Biopsy

  • Not needed for initial diagnosis
  • Recommended before initiating therapy to evaluate unclear cytopenias 1

• Molecular Genetic Testing

  • FISH analysis for cytogenetic abnormalities (prognostic value) 1
  • Testing for IGHV mutation status (prognostic value) 2

Staging After Diagnosis

Once diagnosed, staging is essential using either:

1. Binet Staging System (preferred in Europe):

   • Stage A: Hb ≥10 g/dL, platelets ≥100 × 10^9/L, <3 involved lymphoid areas
   • Stage B: Hb ≥10 g/dL, platelets ≥100 × 10^9/L, ≥3 involved lymphoid areas
   • Stage C: Hb <10 g/dL and/or platelets <100 × 10^9/L 1, 2

2. Rai Staging System:

   • Stage 0 (Low risk): Lymphocytosis only
   • Stage I-II (Intermediate risk): Lymphocytosis with lymphadenopathy and/or organomegaly
   • Stage III-IV (High risk): Lymphocytosis with anemia and/or thrombocytopenia 1, 2

Special Considerations

• Monoclonal B Lymphocytosis (MBL)

  • <5 × 10^9/L monoclonal B lymphocytes
  • No lymphadenopathy, organomegaly, cytopenias, or clinical symptoms
  • Progression to CLL occurs in 1-2% of cases per year 1
  • Important to explain to patients that MBL is not yet leukemia 1

• Small Lymphocytic Lymphoma (SLL)

  • <5 × 10^9/L B lymphocytes in peripheral blood
  • Presence of lymphadenopathy and/or splenomegaly
  • Same immunophenotype as CLL
  • Diagnosis should be confirmed by lymph node biopsy when possible 1

• Relative Lymphocytosis

  • In patients >50 years with persistent relative lymphocytosis (≥50% of differential leukocyte count) but ALC <5 × 10^9/L
  • Consider immunophenotyping to rule out CLL with low lymphocyte count (CLL-LLC) 4

Common Pitfalls to Avoid

1. Assuming lymphocytosis with smudge cells is sufficient for CLL diagnosis

   • These findings can occur in other lymphoproliferative disorders like mantle cell lymphoma 3
   • Always confirm with immunophenotyping

2. Missing CLL with low lymphocyte count

   • Cases with ALC <5 × 10^9/L but characteristic immunophenotype may represent early CLL 4

3. Failure to differentiate from other CD5+ B-cell disorders

   • Always perform comprehensive immunophenotyping and consider additional testing when needed 1, 5

4. Overlooking prognostic markers

   • After diagnosis, evaluate prognostic factors like FISH abnormalities (especially 17p and 11q deletions), IGHV mutation status, CD38 and ZAP-70 expression 2