The use of BRAF-inhibitors as monotherapy and in combination with cytosine arabinoside and 2-chloro-2’deoxyadenosine in pediatric patients with different forms of Langerhans cell histiocytosis

Abstract

Background. Langerhans cell histiocytosis (LCH) is a rare disease that occurs due to abnormal proliferation and expansion of myeloid precursors. The occurrence of mutations in genes that encode key kinases of MAPK-signaling pathway leads to its pathological activation and has been shown the cause of disease. Mutations in BRAF and MAP2K1 genes are the most frequent among LCH patients. The effectiveness of BRAF-inhibitors in LCH patients has been shown in numerous studies.The purpose of the study – analyze the experience of BRAF-inhibitor vemurafenib administration as monotherapy and in combination with cytosine arabinoside (ARA-C) and 2-chloro-2'-deoxyadenosine (2-CdA) in pediatric patients with different forms of LCH.Materials and methods. Fifteen patients with various forms of LCH were enrolled in the study. BRAF mutations were detected in 14 patients, mutation in the MAP2K1 gene was detected in one case. Patients with “risk organ” (RO) involvement were included in the first group (n = 9). These patients received combined therapy with vemurafenib and ARA-C/2-CdA. Patients without RO involvement, included in group 2 (n = 6), received vemurafenib as monotherapy. The assessment of the response to the therapy in group 1 was carried out in accordance with the DAS scale, in group 2 in accordance with the RECIST v1.1. The toxicity assessment in both groups was carried out in accordance with the CTCAE v5.0.Results. All patients in group 1 achieved non-active disease status with a median of 35 (28–61) days. In group 2 partial response to vemurafenib was achieved in 5 cases. Relapse after targeted therapy termination was diagnosed in two patients. Photodermatitis was the most common side effect of targeted therapy.Conclusions. The use of vemurafenib was effective in both groups. There were no cases of grade III–IV toxicity according to CTCAE v5.0 associated with vemurafenib administration in this study. The combination of vemurafenib and ARA-C/2-CdA showed high efficacy and good tolerability in group 1. Two cases of disease relapse after targeted therapy cessation in group 2 show that the monotherapy approach does not always allow to achieve long-term remission in LCH patients.