What is the role of bone marrow aspiration in the diagnosis of hairy cell leukemia (HCL)?

Updated: Sep 16, 2018
  • Author: Emmanuel C Besa, MD; Chief Editor: Koyamangalath Krishnan, MD, FRCP, FACP  more...
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Answer

The immunophenotypic profile of HCL is characterized by the clonal expansion of B‐cells with bright CD19, CD20, CD22, and CD200 expression. Hairy cells are usually negative or dim for CD5, CD23, CD10, CD79b, and CD27 but positive for CD11c, CD103, CD123, and CD25. A proposed immunological score gives one point to each of the last four markers when they are expressed. A score of 3 or 4 is observed in 98% of HCL cases, whereas in other HCL‐like disorders, the score is usually 0 or 1. [13]

The somatically acquired V600E mutation of the BRAF gene is present in nearly all patients with HCL and represents a reliable marker. [18]  BRAF- V600E can be reliably detected at the protein level by immunohistochemical stain using a mutant protein-specific antibody. [19]

A study by Tiacci et al examined the use of a test for genetically-based diagnosis of HCL. The molecular assay determines the presence of the BRAF-V600E mutation in order to differentiate between HCL and other disorders (eg, splenic marginal zone lymphoma, hairy cell leukemia variant). The study found that the molecular assay was a powerful tool for enhancing diagnostic accuracy. [20]

Genomic analysis of de novo vemurafenib-resistant classic HCL identified a novel gain-of-function mutation in IRS1 and losses of NF1 and NF2, each of which contributed to treatment resistance. [21]


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