We assessed phospho-ERK expression in 37 patients with hairy cell leukemia and 44 patients with neoplasms mimicking hairy cell leukemia (40 splenic marginal zone lymphoma, 2 hairy cell leukemia-variant and 2 splenic lymphoma/leukemia unclassifiable) using immunohistochemistry on routine biopsies and/or Western blotting on purified leukemic cells, and correlated the phospho-ERK status with the BRAF-V600E mutation status.
BRAF p.V600E mutation was present in all HCL cases and absent in all HCL-v. Our data support the recent finding that BRAF p.V600E mutation is universally present in HCL.