Langerhans cell histiocytosis: Version 2021.

Area of Science:

• Immunology
• Oncology
• Genetics

Background:

• Langerhans cell histiocytosis (LCH) presents as granulomatous lesions with clonal CD207+ dendritic cells.
• Clinical presentations vary, but LCH lesions are histologically similar, complicating classification as immune or neoplastic.
• Historically, LCH classification has challenged optimal clinical strategies.

Purpose of the Study:

• To investigate the role of MAPK pathway mutations in LCH pathogenesis.
• To explore the implications of these mutations for disease classification and therapeutic development.
• To re-evaluate LCH and related histiocytic disorders as myeloid neoplastic disorders.

Main Methods:

• Analysis of somatic mutations in MAPK pathway genes in LCH and related histiocytic disorders.
• Investigation of the impact of MAPK pathway activation on myeloid differentiation, cell migration, and apoptosis.
• Correlation of mutation timing and myeloid differentiation stage with disease extent and neurodegeneration risk.

Main Results:

• Activating somatic mutations in MAPK pathway genes, particularly BRAFV600E, are found in nearly all LCH cases.
• MAPK activation in LCH precursor cells promotes myeloid differentiation, inhibits migration, and prevents apoptosis, leading to pathological dendritic cell accumulation.
• Recurrent MAPK pathway mutations are also identified in juvenile xanthogranuloma, Erdheim-Chester disease, and Rosai-Dorfman disease.

Conclusions:

• New insights into pathogenesis support reclassifying LCH and related histiocytic disorders as myeloid neoplasms.
• Understanding the cell of origin and specific mutations can inform personalized therapeutic strategies.
• Continued research into these myeloid neoplasms will identify novel therapeutic targets.