Bouroncle BA, Wiseman BK, Doan CA. Leukemic reticuloendotheliosis. Blood. 1958;13(7):609-630.

In this paper, Bertha A. Bouroncle and colleagues describe for the first time the clinical and pathologic features of hairy cell leukemia. The term "leukemic reticuloendotheliosis" proposed a cell of origin that was misplaced, but the remainder of scientific work described is completely consistent with our current understanding of the disease. Specifically, this paper describes the frequency of hairy cell leukemia among all adult leukemias and characterizes the pathology using several techniques still applied today. Furthermore, examining the clinical features of these patients, the authors describe the signs and symptoms of the disease, complications that arise, and expected outcome without modern therapy available today.

Current Therapy and New Directions in the Treatment of Hairy Cell Leukemia: A Review.

Hairy cell leukemia (HCL) is a chronic B-cell leukemia noted for an indolent course that ultimately results in cytopenias and massive splenomegaly. Whereas treatment with the nucleoside purine analogues cladribine and pentostatin results in lengthy remissions in nearly all patients with HCL, most patients will experience relapse while a small percentage of patients' disease fails to respond to therapy in the first place. Retreatment with a purine nucleoside analogue often leads to an effective but limited response. For decades, few other viable therapeutic options were available to these patients who required retreatment. Recently, new insights into the mechanism of disease of HCL have led to research in new potential treatment agents, either alone or with a purine nucleoside analogue. Clinical trials with rituximab, bendamustine, and conjugate immunotoxins will reveal what role these therapies will have in HCL treatment. A better understanding of the BRAF/MEK/ERK pathway and the B-cell signaling pathway has allowed further exploration into the novel drugs vemurafenib, dabrafenib, trametinib, and ibrutinib.

Historical overview of hairy cell leukemia.

Since its discovery in 1923 and further characterization in 1958, hairy cell leukemia (HCL) has undergone enormous advances in the understanding of the biology and treatment of the disease. Initially a uniformly fatal disease, new therapies in rapid succession transformed HCL into a chronic disease with a normal life expectancy in many cases. More recently, the identification of BRAFV600E mutations in the majority of patients with classic HCL have enabled targeted therapies as a therapeutic option. Additional discoveries into the biology of the disease have identified new subtypes of HCL. Modern approaches to the evaluation and treatment of HCL include detailed molecular analysis which informs therapeutic options, which may consist of traditional therapies such as purine nucleoside analogs, or targeted therapies with antibodies, BTK inhibitors, or BRAF inhibitors, or combination therapy. Because HCL is a rare disease, continued progress depends on patients being enrolled on clinical trials whenever possible.

Hairy cell leukemia: Past, present and future.

This brief review highlights the sequence of therapeutic milestones and advances in our understanding of the biology of hairy cell leukemia (HCL) with a focus on recent molecular findings and how these may be applied to improve disease outcomes in the future. Targeted therapy is discussed in the context of the recently identified BRAF mutation and other genetic findings.

The pathophysiology of the hairy cell.

HCs are clonal late B cells that are related to memory cells and display specific features of activation. Many of the distinctive features of HCs (eg, morphology, TRAP) are related to this specific activation. Many of the distinctive histologic features of HCL can be related to constitutive production of cytokines (eg, FGF, fibrosis) and to the expression/activation of adhesion receptors (eg, alpha(4)beta(1), alpha(5)beta(1) and alpha(v)beta(3) integrins, CD44v3). HCs usually have mutated IGVH genes and have no consistent or specific chromosome abnormalities (5q additions and 7q deletions in a minority). The signals that are responsible for several of the phenotypic features of HCs have been identified, but the nature of the underlying oncogenic events remains unknown.

Splenectomy, interferon, and treatments of historical interest in hairy cell leukemia.

The evolution and "lessons learned" for therapeutic options and approaches in HCL, which subsequently evolved into the adenosine deaminase inhibitors as the treatment of choice, has been intriguing. The contributions to patient care and individual patient lives have been remarkable. Observation, splenectomy, and recombinant interferon are potential therapeutic are alternatives in select patients as initial therapy, and as therapeutic alternatives in the 10% of patients who have progressive disease after the purine nucleoside analogs.

Purine analogues: rationale for development, mechanisms of action, and pharmacokinetics in hairy cell leukemia.

Cladribine is effective therapy for HCL, and there are several ways to achieve the adequate concentrations of the active metabolites in relevant cells, without the need for long-term continuous infusions. This simplifies therapy, although careful control of patients is required during and after treatment in most instances because of the significant activity of the drug on leukemia cells of various types and also on lymphoid cells and normal stem cells.