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.