Relevant information on Langerhans cell histiocytosis development and course in children is presented. The current concepts of disease pathogenesis, principles of its severity evaluation, patients stratification into risk groups, as well as of clinical course features are described. Modern approaches to the disease treatment via targeted therapy are summarized and analyzed.

This article discusses the potential of droplet digital polymerase chain reaction (PCR) for the diagnostic detection and monitoring of the allelic load of the BRAF V600E mutation in circulating cell-free DNA and myeloid progenitor cell population in the bone marrow of patients with Langerhans cell histiocytosis (LCH). Droplet digital PCR may serve as a useful tool for the monitoring of minimal residual disease and improve our understanding of the pathogenesis of Langerhans cells histiocytosis. The study was approved by the Independent Ethics Committee and the Scientific Council of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology.

Relevance. Juvenile xanthogranuloma (JXG) is the most common form of non-Langerhans cell histiocytic disorder. Cutaneous forms of the disease spontaneously regress within a few years, while systemic forms of JXG require treatment and may pose a threat to the lives of patients. Due to the lack of unified approach to the treatment of multisystem forms of JXG, the question of effective therapy tactics remains unresolved. The most common approach is to use Langerhans cell histiocytosis (LCH) treatment regimens for JXG. With the understanding of the leading role of mutations in the MEK-ERK signaling pathway in the pathogenesis of JXG, targeted therapy, BRAF- and MEK-inhibitors, are increasingly being considered in the treatment of JXG.Clinical cases. We present two cases of multisystem JXG with central nervous system (CNS) lesions. The first patient with CNS and skin lesions was treated with chemotherapy, developed for the treatment of multisystem LCH, which allowed us to obtain an effect “active disease better” (AD better). The second JXG patient with brain, lungs, bones, and adrenal gland lesions, combined targeted therapy with BRAF- and MEKinhibitors, vemurafenib and cobimetinib, resulted in a “non active disease” (NAD) effect.Conclusion. Multisystem form of JXG with CNS involvement is a rare oncological disease, the therapy of which has not been developed. With the introduction of molecular genetic profiling technology, it became possible to obtain NAD effect using targeted therapy.

Background. There are increasing data of targeted therapy efficacy of different types of Langerhans cell histiocytosis (LCH) with inhibitors of BRAF-specific serin-threonine kinase (BRAF-inhibitors) in cases with BRAF V600E mutation published last years. At the same time there are no published data of use of inhibitors of MAPK/ERK pathway (MEK-inhibitors) in pediatric patients with BRAF-negative forms of LCH.Purpose of the study is to evaluate efficacy and safety of MEK-inhibitor (cobimetinib) in eight pediatric BRAF V600E-negative refractory LCH patients.Materials and methods. The study included 8 children with various forms of LCH. All patients received therapy according to the LCH-IV protocol and were diagnosed with progression of LCH during or after termination of the treatment. The response to the therapy was assessed in accordance with the international scale Response Evaluation Criteria in Solid Tumors (RECIST v.1.1). The assessment of the toxicity was performed in accordance with the international scale of Common Terminology Criteria for Adverse Events (CTCAE v.5.0).Results. Complete response was not achieved in any patient. Partial response was established in 5 cases. One patient was diagnosed with disease progression in three months after termination of the therapy. The incidence of adverse events was high.Conclusion. Cobimetinib therapy is effective in BRAF V600E-negative refractory pediatric LCH patients. The response to the treatment can be delayed. All cases of the toxicity were dose depended and successfully resolved after dose correction. Further research is needed to define duration of treatment and optimal dosage.