MM250707: Splenic marginal zone lymphoma (SMZL)
This week’s case featured a patient who presented with fatigue and palpable splenomegaly. A routine full blood count revealed:
- WBC: 48.35 ×10⁹/L ↑
- Hb: 94 g/L ↓
- RBC: 3.34 ×10¹²/L ↓
- MCV: 71.4 fL ↓
- MCH: 21.7 pg ↓
- Platelets: 185 ×10⁹/L
- Lymphocytes: 75% (absolute: 36.26 ×10⁹/L)
These results show a marked lymphocytosis, accompanied by anaemia and microcytosis, prompting a blood film and flow cytometry for further classification.
The film showed numerous small to medium-sized lymphocytes with irregular or “villous” cytoplasmic projections; a classic clue in certain low-grade B-cell lymphomas.
Flowcytometry results showed:
- Positive: CD19, CD20, CD22, CD11c, CD79b, surface IgM
- Negative: CD5, CD10, CD23, CD25, CD103, CD123, Annexin A1
This immunophenotype is consistent with a mature, non-class switched B-cell population, showing strong surface IgM and lacking markers typically seen in other lymphomas.
Critically, the absence of CD103, CD123, and Annexin A1 helped to exclude classical hairy cell leukaemia (HCL), which usually expresses all three.
The combination of splenomegaly, villous lymphocytes on film, and a CD103–/CD123–/Annexin A1– phenotype confirmed the diagnosis of Splenic Marginal Zone Lymphoma (SMZL) a rare, indolent B-cell lymphoma typically involving the spleen, bone marrow, and peripheral blood.
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2 Comments
Can it be SBL with prominent nucleoli or vHCL
Great question and both are valid considerations in the differential.
Splenic B-cell lymphoma/leukaemia, unclassifiable (SBL) with prominent nucleoli does overlap morphologically with splenic marginal zone lymphoma (SMZL) and variant hairy cell leukaemia (vHCL). When nucleoli are visible and the projections are less fine than in classical HCL, vHCL can be especially difficult to rule out based on morphology alone.
What helps steer this case away from vHCL are the flow cytometry findings:
– Negative for CD103, CD123, and Annexin A1
– Strong surface IgM and CD20 positivity, but no CD25
These features are atypical for vHCL, which usually expresses CD103, CD123, and often Annexin A1 (even in variant cases).
As for SBL, it remains a valid label when the immunophenotype is ambiguous — but in this case, the profile aligns closely with SMZL.
Ultimately, clinical correlation, splenic histology (if available), and molecular testing (e.g., NOTCH2 or MAP2K1 mutations) can help resolve these edge cases.
Thanks for raising an important diagnostic nuance!