Hairy Cell Leukemia (HCL)

Hairy cell leukemia is a mature B cell neoplasm. It is usually classified as a sub-type of chronic lymphoid leukemia (CLL)  for convenience. It is uncommon, representing about 2% of all leukemias, or less than a total of 2000 new cases diagnosed each year in North America and Western Europe combined.

Sample Cases

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Case Name (click on case name to open)	Comments	Size
HCL1	Hairy Cell	3.76 MB
case 12	Classic HCL This case was kindly provided by the ASCP Press. It is part of Flow Cytometry in Clinical Diagnosis by John Carey, Phil McCoy and David Keren.	741 kB
case 13	HCL This case was kindly provided by the ASCP Press. It is part of Flow Cytometry in Clinical Diagnosis by John Carey, Phil McCoy and David Keren.	1027 kB
case 14	CD5+ HCL This case was kindly provided by the ASCP Press. It is part of Flow Cytometry in Clinical Diagnosis by John Carey, Phil McCoy and David Keren.	861 kB

Epidemiology

This disease is rare, with fewer than 1 in 10,000 people being diagnosed with HCL during their lives. Although most patients are white males over the age of 50, it has been diagnosed in at least one teenager . Men are four to five times more likely to develop hairy cell leukemia than women. It does not appear to be hereditary, although occasional familial cases have been reported, usually showing a common HLA type.

Possible causes

The cause is unknown, but, in general, believed not to be caused by tobacco, ionizing radiation, pesticides, or industrial chemicals other than possibly diesel. Farming and gardening appear to increase the risk in some studies. The possibility that HCL is caused by a random accident during routine cell division cannot be ruled out.

Morphology

Abnormal white blood cells bearing hair-like projections from the cytoplasm are seen on blood film examination or bone marrow biopsy.  These are medium sized cells with pale cytoplasm, oval and often reniform or bean-shaped nuclei and clumped or evenly distributed chromatin.      

Example of HCL cells	Example of HCL cells

Immunophenotyping

Hairy cells are larger than normal and positive for CD19, CD20, CD22, CD11c, CD25, CD103, and FMC7. Hairy cell leukemia-variant (HCL-V), which shares some characteristics with B cell prolymphocytic leukemia (B-PLL), does not show CD25 (also called the Interleukin-2 receptor, alpha). Because a patient could have more than one similar disease, it is also necessary to rule out the presence of leukemias and lymphomas such as SMZL or B-PLL.       

Note the red lymphocyte population and the variation in size (higher SSC) requiring further investigation.

 

The majority of the lymphocytes (red)express a moderate-bright monoclonal kappa light chain expansion.	The lymphocyte brightly express CD20 and FMC-7. CD11c and CD103 are characteristic of HCL.