Both variant and IGHV4-34–expressing hairy cell leukemia lack the BRAF V600E mutation

Abstract

Abstract Recently, the BRAF V600E mutation was reported in all cases of hairy cell leukemia (HCL) but not in other peripheral B-cell neoplasms. We wished to confirm these results and assess BRAF status in well-characterized cases of HCL associated with poor prognosis, including the immunophenotypically defined HCL variant (HCLv) and HCL expressing the IGHV4-34 immunoglobulin rearrangement. Fifty-three classic HCL (HCLc) and 16 HCLv cases were analyzed for BRAF, including 5 HCLc and 8 HCLv expressing IGHV4-34. BRAF was mutated in 42 (79%) HCLc, but wild-type in 11 (21%) HCLc and 16 (100%) HCLv. All 13 IGHV4-34+ HCLs were wild-type. IGHV gene usage in the 11 HCLc BRAF wild-type cases included 5 IGHV4-34, 5 other, and 1 unknown. Our results suggest that HCLv and IGHV4-34+ HCLs have a different pathogenesis than HCLc and that a significant minority of other HCLc are also wild-type for BRAF V600.