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.