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.

Here we report a clinical case of a patient with BRAF-positive Langerhans cell histiocytosis treated with combination therapy including trametinib. As the patient was undergoing long-term therapy with a BRAF inhibitor, his underlying disease reactivated. Hence it was suggested that the child might have become resistant to the treatment as a result of a subclonal mutation. It was concluded that this event undermined the efficacy of long-term therapy with BRAF inhibitors and highlighted the need for further study of possible molecular genetic mechanisms involved in the pathogenesis of Langerhans cell histiocytosis, as well as the need for the development of new treatment approaches. The patient's parents gave consent to the use of their child's data, including photographs, for research purposes and in publications.

Malignant rhabdoid tumor (MRT) is a rare malignant neoplasm of childhood, characterized by an aggressive course and an extremely unfavorable prognosis. The frequency of MRT outside the central nervous system (extracranial MRT) is 0.02–0.03 per 100,000 children. In most cases, MRT is based on an inactivating mutations of the tumor suppressor gene SMARCB1, which leads to the absence of expression of the SMARCB1 ((INI1/hSNF5/BAF47) protein in tumor cells. Aberrations of the SMARCA4 gene, which is an extremely rare molecular event, have been described among the MRTs expressing SMARCB1 (INI1). Few case reports have been described in the international literature.This article contains a description of a clinical case of a patient diagnosed with soft tissue MRT with SMARCA4 gene alteration. The distinctive features of the presented case are the congenital nature of the tumor, atypical localization, and extremely aggressive clinical course of the disease. On the example of the described clinical case, diagnostics of SMARCA4-associated MRT are presented, as well as the place of molecular methods in diagnosis verification. In addition, it is highlighted that the detection of somatic changes in the SMARCB1 and SMARCA4 genes requires additional investigation of their germinal status to exclude or confirm the rhabdoid tumor predisposition syndrome.