Disseminated, yet dissembled: Rare infections behind the veil of classical hairy cell leukemia

How I treat refractory/relapsed hairy cell leukemia with BRAF inhibitors

Hairy cell leukemia (HCL) responds very well to frontline chemotherapy with purine analogs (cladribine and pentostatine). However, approximately half of patients experience 1 or more relapses, which become progressively resistant to these myelotoxic and immunosuppressive agents. At progression, standard therapeutic options include a second course of purine analogs alone or in combination with rituximab and, upon second relapse, therapy with the anti-CD22 immunotoxin moxetumomab pasudotox. Furthermore, blockade of the mutant BRAF-V600E kinase (the pathogenetic hallmark of HCL) through orally available specific inhibitors (vemurafenib or dabrafenib) effaces the peculiar morphologic, phenotypic, and molecular identity of this disease and its typical antiapoptotic behavior and is emerging as an attractive chemotherapy-free strategy in various clinical scenarios. These include patients with, or at risk of, severe infections and, in a highly effective combination with rituximab, patients with relapsed or refractory HCL. Other treatments explored in clinical trials are BTK inhibition with ibrutinib and co-inhibition of BRAF (through dabrafenib or vemurafenib) and its downstream target MEK (through trametinib or cobimetinib). Here, we focus on our experience with BRAF inhibitors in clinical trials and as off-label use in routine practice by presenting 3 challenging clinical cases to illustrate their management in the context of all available treatment options.

Inhibitor of BRAFV600E Mutation as a Treatment Option for Hairy Cell Leukemia With Deep Neutropenia and Infectious Complications

Standard therapy in hairy cell leukemia (HCL) is often impossible at the time of deep neutropenia/agranulocytosis with or without infectious complications; it is thus a complex therapeutic problem. Vemurafenib has been used to treat resistant HCL since 2012. Because vemurafenib does not have a myelotoxic effect, we thought that it could be used to treat HCL associated with deep neutropenia/agranulocytosis with or without the development of infectious complications as a preliminary stage before treatment with cladribine. We conducted a retrospective analysis of treatment with vemurafenib followed by a standard course of cladribine provided to 22 patients with deep neutropenia/agranulocytosis with or without infectious complications at diagnosis. Vemurafenib was provided to 22 patients with HCL. The response to therapy was evaluated by complete blood cell count (absolute neutrophil count [ANC], hemoglobin concentration, platelet count, absence of hairy cells), spleen size (assessed by ultrasound), and reduce infectious complications. After that, a standard course of cladribine was provided. Among the 22 patients, the male/female sex ratio was 2:1, and median (range) age was 52 (24-78) years. There were 7 patients with severe infectious manifestations admitted to the intensive care unit, including 1 patient during extracorporeal membrane oxygenation. The median (range) ANC at diagnosis was 0.3 (0.04-0.7) × 10⁹/L. Vemurafenib was provided at a dosage of 240 mg 1 or 2 times a day. In 20 patients, vemurafenib was provided for 3 months or more. In 1 case, the effect was not obtained during 1 month of treatment, and the patient died from severe infectious complications during prolonged agranulocytosis. In 21 patients treated with vemurafenib, an increase of ANC was observed and the infectious complications resolved, thus allowing the application of cladribine therapy. After a standard course (0.1 mg/kg per day for 7 days) of cladribine chemotherapy, 18 patients (90%) experienced complete clinical remission and 2 patients (10%) experienced partial remission with residual splenomegaly. In 1 patient, vemurafenib therapy was still ongoing 2 months after initiating therapy. In cases of proven BRAF^V600E mutation, vemurafenib can be successfully used as an effective preliminary therapy in patients with deep neutropenia/agranulocytosis with or without infectious complications before standard therapy with purine analogs.