Hairy cell leukaemia: BRAF V600E, the dry tap and the red-pulp spleen
- Lesion
A rare, slow B-cell leukaemia of middle-aged men with fine hair-like projections, a huge spleen and low blood counts.
What it is
Hairy cell leukaemia is an uncommon indolent B-cell neoplasm named for the fine cytoplasmic projections of its cells. Nearly all cases carry the activating BRAF V600E mutation. The cells infiltrate the marrow, splenic red pulp and liver sinusoids rather than lymph nodes, causing massive splenomegaly and pancytopenia. Marrow aspiration often fails because the cells are trapped in reticulin fibres.
Structure
- Blood: small numbers of cells with oval or bean-shaped nuclei and pale blue cytoplasm with hair-like projections.
- Marrow biopsy: cells with clear cytoplasm spaced apart (fried-egg look) in a reticulin mesh.
- Spleen: red pulp expanded, white pulp effaced, blood lakes.
Step by step
- A mature B cell acquires BRAF V600E, constantly activating the MAPK/ERK pathway.
- The clone homes to marrow, splenic red pulp and liver.
- Marrow infiltration with reticulin fibrosis lowers production; the large spleen traps blood cells.
- Pancytopenia leads to infections, anaemia and bleeding.
Markers
- CD11c
- CD25
- CD103
- Annexin A1
- BRAF V600E
- TRAP
Clinical notes
- Middle-aged men (male-to-female ratio about five to one) with splenomegaly and cytopenias.
- Very responsive to purine analogue chemotherapy, with long remissions.
Test yourself
Think of the answer, then tap the question to see it.
Which mutation is nearly universal in hairy cell leukaemia?
BRAF V600E.
Why is a marrow aspirate often a dry tap?
The tumour cells are enmeshed in reticulin fibres and cannot be aspirated; a biopsy is needed.
Which part of the spleen do hairy cells infiltrate?
The red pulp, producing massive splenomegaly.
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Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Hairy Cell Leukemia Treatment (PDQ®)–Patient Version (National Cancer Institute (NCI), 2026).
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Representative model, for educational purposes only.