Hairy Cell Leukemia

A 47-year-old female presented with pancytopenia and monocytopenia in peripheral blood:

Peripheral Blood Counts
 RBC
2.72x10^12/L  
 Hemoglobin
 10.1 g/dL  
 Hematocrit
 29%  
 MCH
 37 pg  
 MCV
 106.3 fL  
 MCHC
 34.8 g/dL  
 WBC
 3.0 x 10^9/L  
 Absolute neutrophil count
 0.5 x 10^9/L  
 Absolute lymphocyte count
 2.4 x 10^9/L  
 Aboslute moncyte count
 0.1 x 10^9/L  
 Absolute eosinophil count
 0.1 x 10^9/L  
 Absolute basophil count
 0 x 10^9/L  
 Platelets
 44 x 10^9/L  
 MPV
 8.3 fL  

Peripheral Blood shows a subset of atypical lymphocytes with hairy-like cytoplasmic projection.

Atypical lymphoid cells are positive for TRAP

Bone Marrow Aspirate
 Blasts
0.10% 
 Promyelocvtes
0% 
 Metaƨmyelocytes. bands, segmented neutrophils
2.20% 
 Erythroid precursors:
13% 
 Lymphoid cells:
82.20% 
 Monocytes:
0.80% 
 Plasma cells:
1.70% 
 Eosinophils:
0.30% 
 Basophils:
0.10% 
 Mast cells:
0.30% 

Bone marrow aspirate is remarkable for 82.2% lymphoid cells many with moderate to large amount of cytoplasm and irregular cytoplasmic hairy-like projections in a large subset.

Flow Cytometry shows kappa light chain restricted B-cell population co-expressing CD20, CD103, CD11c, CD25.

Bone Marrow Biopsy is hypercellular for patient's age (70-80 %) and remarkable for extensive replacement of the bone marrow space by a population of neoplastic lymphoid cells which comprise approximately 80-90% of the nucleated bone marrow cells.

There is a large CD20+ ( >85% of the nucleated bone marrow cells), Annexin A1+, BCL2+, variably Cyclin D1+, CD10 negative neoplastic B-lymphoid population with a rather low proliferation rate (less than 5%) in the bone marrow.

The diagnosis of this case is: Hairy cell leukemia with extensive bone marrrow involvement.

Hairy cell leukemia is a rare neoplasma of small mature B lymphoid cells (post-germinal center stage, arrested at some point during isotype switching), comprising 2% of lymphoid leukemias. Patients are predominantly middle-aged to elderly adults with a median age of 50 years. Tumor cells are located predominantly in the bone marrow and spleen with a small number of circulating "hairy" cells. 

The bone marrow effacement is of variable extent. The primary pattern is interstitial or patchy infiltration of widely-spaced lymphoid cells with oval or indentaed nuclei with abundant cytoplasm and prominent cell borders taking a "fried-egg" appearance. An increased reticulin fiber is common and often results in a "dry-tap".

Hairy cell leukemia is uniquely sensitive to either alpha-interferon or nucleosides such as pentostatin and cladribine. Anti-CD20, anti-CD22, and anti-CD25 are the new agents available recently of variant indications. Prolonged remission may also result from splenectomy, but this is uncommon. The overal 10-year survival rate exceeds 90%.

 

Contributed by Jianhong Li, MD and Dr. Diana Treaba

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