Expression and clinical correlation of cathepsin S, programmed cell death-1 ligand 1, and BRAFV600E mutation in children with Langerhans cell histiocytosis.

Background: The expression and clinical correlation of BRAFV600E mutation and programmed cell death-1 ligand 1 (PD-L1) in children with Langerhans cell histiocytosis (LCH) have been reported, but the conclusions of previous studies are inconsistent. In addition, it has been reported that elevated cathepsin S (CTSS) expression is associated with various cancers. However, there is currently no research on the correlation between CTSS and LCH. The aim of this study was to reassess the clinical correlation of BRAFV600E mutation and PD-L1 in pediatric LCH and to investigate the expression and clinical correlation of CTSS in children with LCH.

Methods: A total of 35 tissue samples were analyzed for the BRAFV600E gene mutation using droplet digital polymerase chain reaction, and 31 tissue samples were examined for CTSS and PD-L1 by immunohistochemistry. In addition, the clinical characteristics and prognosis of these 35 pediatric patients were analyzed and summarized.

Results: The incidence of BRAFV600E gene mutation was 34.3% (12/35). The occurrence of BRAFV600E gene mutation was significantly associated with age ≤ 2 years and involvement of central nervous system risk sites (66.7% and 72.7%, respectively). The expression rate of PD-L1 was 35.5% (11/31), and it was significantly correlated with cutaneous involvement (100%, 3/3). PD-L1 expression was unrelated to BRAFV600E gene mutation. Neither BRAFV600E gene mutation nor PD-L1 expression had a significant impact on disease progression/reactivation and initial 6-week treatment response. CTSS was expressed positively in the lesion tissues of all 31 children with LCH. The H-scores of CTSS were significantly associated with age ≤ 2 years. CTSS had no significant effect on the initial 6-week treatment response, disease progression/reactivation, BRAFV600E gene mutation, or PD-L1 expression.

Conclusions: CTSS is positively expressed in LCH, and its expression level is associated with onset age ≤ 2 years. BRAFV600E gene mutation, PD-L1, and CTSS may not be associated with the prognosis of LCH.