malignant hematology

Q: What is the hallmark molecular mutation in classic Hairy Cell Leukemia (HCL)?

A: BRAF V600E mutation

• Present in ~80–100% of classic HCL

• Activates the MAPK pathway

• Diagnostic and therapeutic target (vemurafenib, dabrafenib)

Q: Which CBC abnormality is most characteristic of classic HCL?

A: Monocytopenia ⭐ (board favorite)

Q: Which flow cytometry markers are characteristic of classic HCL?

• CD19+

• Bright CD20

• CD22+

• FMC7+

• Bright CD11c

• CD25+

• CD103+

• CD123+

Q: Which immunohistochemical markers are positive in classic HCL?

A:

• Annexin A1 ⭐

• TRAP

• CD20

• DBA44

• Cyclin D1 (subset)

• VE1 (BRAF V600E)

 Which marker is highly specific for classic HCL and helps distinguish it from HCL variant?

Annexin A1

Which mutation is absent in HCL variant (SBLPN)?

BRAF V600E

Q: What is the preferred first-line treatment for symptomatic classic HCL?

Cladribine + Rituximab (concurrent)

Q: How is relapsed HCL managed?

A:

• Relapse ≥2 years: Repeat purine analog

• Relapse <2 years: Vemurafenib ± rituximab, Dabrafenib + trametinib, or clinical trial

HCL