Updated consensus guidelines for the diagnosis and management of patients with hairy cell leukemia (HCL) and HCL-variant

: Hairy cell leukemia (HCL) and hairy cell leukemia variant (HCLv) are distinct, rare, chronic splenic B cell lymphomas/leukemias that partially overlap in clinico-pathological presentation but differ in genetic basis, prognosis, and management. HCL is caused by the BRAF-V600E kinase-activating mutation in >95% of patients, usually has excellent responses to chemotherapy with purine analogs and is also amenable to BRAF inhibitor-based targeted treatments. In contrast, HCLv lacks BRAF-V600E, requires combined therapy with purine analogs plus rituximab and generally shows less-durable responses. Here, an international team of hematologists expert on these rare diseases was convened by the Hairy Cell Leukemia Foundation to update the previous guidelines (published in 2017) by providing a summary of current methods to diagnose and manage patients with HCL and HCLv, as well as a prospective on newer targeted therapies to further improve outcome.