BRAFV600E Mutation in a Histiocytic Sarcoma Arising From Hairy Cell Leukemia

Our patient, a white man with a 26-year history of hairy cell leukemia (HCL), was initially diagnosed in 1986 when he was 48 years old. He was first treated with splenectomy and interferon therapy. Two subsequent relapses, 17 and 20 years after the initial diagnosis, were successively treated with 2-chlorodeoxyadenosine (2-CdA) with a good response on the basis of hairy cell blood count and flow cytometry. Two years later, the patient relapsed for a third time. He was treated with three courses of rituximab (375 mg/m 2 per week for 3 weeks) without any response. He then received 10 courses of pentostatin and went into complete remission after a normal bone marrow evaluation. Complete remission was maintained for 3 years, after which a new relapse occurred. He was treated with an additional course of 2-CdA, which achieved a good response. One year later, the blood cell count was normal, and 0.13% of circulating hairy cells were detected by flow cytometry.