Partial response in hairy cell leukemia with vemurafenib despite early discontinuation due to agranulocytosis.

Vemurafenib is an oral BRAF kinase inhibitor approved since 2012 for the treatment of patients with unresectable or metastatic melanoma with BRAF mutations. Vemurafenib also demonstrated efficacy for patients with hairy cell leukemia genetically characterized by BRAF mutation. Here, we report the case of a 38-year-old female patient without any previous medical history who experienced agranulocytosis associated with erythrodermia after vemurafenib initiation for the treatment of hairy cell leukemia. Agranulocytosis was confirmed with bone marrow examination. Vemurafenib was considered the most probable drug responsible for this agranulocytosis and was thus stopped. We observed a full neutrophils recovery 10 days after vemurafenib cessation without any haematopoietic growth factors. A bone marrow biopsy performed 1 month after aplasia ending showed a good partial response with less than 5% of hairy cells remaining. To our knowledge, this is the first case ever described by vemurafenib-induced agranulocytosis. Thus, physicians should be warned about this risk given the growing number of patients treated with vemurafenib.