Experience with the Use of B-RAF Inhibitor Vemurafenib in the Treatment of Hairy Cell Leukemia

Background. The standard and effective treatment of hairy cell leukemia (HCL) involves purine analogs, interferon-α (IFN-α) administration, and splenectomy. However, primary resistant HCL and early relapses (within 2–3 years after achieving remission) remain clinical challenges. Due to myelotoxicity of cladribine and slow effect of IFN-α, these drugs can be administered neither in deep neutropenia/agranulocytosis patients (especially in case of infectious complications) nor in patients with IFN-α allergy/intolerance. Aim. To report clinical experience with vemurafenib, a B-RAF inhibitor, in HCL with BRAFV600E mutation in treatment-resistant patients with contraindications to standard therapy. Materials & Methods. The study enrolled 39 HCL patients aged 24–78 years (median 55 years), 13 women and 26 men. HCL was diagnosed in accordance with the WHO 2017 criteria. Vemurafenib 240 mg was administered once or twice a day within 3 months. Three groups of patients were analyzed: those with early relapses and resistant HCL (n = 7), those with deep neutropenia/agranulocytosis (with and without infectious complications, n = 29), and those with IFN-α intolerance (n = 3). Results. In 6 (86 %) out of 7 patients from group 1 (with early relapses and resistant HCL) a complete course of treatment was carried out, which included vemurafenib with subsequent standard cladribine chemotherapy and further consolidation with rituximab. Complete remission was achieved in 5 (71 %) patients, and partial remission was achieved in 1 (14 %) patient. The 7th patient was a non-responder. In 28 (97 %) out of 29 patients from group 2 with deep neutropenia/agranulocytosis, hematologic recovery was reported which allowed for further basic treatment with cladribine. In 1 patient vemurafenib appeared to be ineffective. In 3 patients from group 3 with IFN-α intolerance, vemurafenib administration was used as a stage of treatment preceding cladribine therapy. Cladribine treatment resulted in complete remission in 2 (67 %) patients and partial remission in 1 (33 %) patient. Conclusion. In HCL with BRAFV600E mutation, low-dose vemurafenib can be effective in patients with relapsed/refractory disease as well as deep neutropenia with life-threatening infectious complications. In addition to that, vemurafenib administration can be used in cases of IFN-α intolerance as a stage of treatment of HCL with BRAFV600E mutation which precedes the basic cladribine therapy.