Updated consensus guidelines for the diagnosis and management of patients with HCL and HCL variant

Hairy cell leukemia (HCL) and HCL variant (HCLv) are distinct, rare, and chronic splenic B-cell lymphomas/leukemias that partially overlap in clinicopathologic presentation but differ in genetic basis, prognosis, and management. HCL is caused by the BRAF-V600E kinase-activating mutation in >95% of the patients, usually has excellent responses to chemotherapy with purine analogues, and is also amenable to BRAF inhibitor-based targeted treatments. In contrast, HCLv lacks BRAFV600E mutation, requires combined therapy with purine analogues in addition to rituximab, and generally shows less durable responses. Here, an international team of hematologists, experts 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 outcomes.