title: Mutually exclusive extracellular signal-regulated kinase pathway mutations are present in different stages of multi-focal pulmonary Langerhans cell histiocytosis supporting clonal nature of the disease.
abstract: OBJECTIVE
  Pulmonary Langerhans cell histiocytosis (PLCH) is an idiopathic cigarette smoking-related disorder of the lung. Molecular changes in cellular or fibrotic stages of PLCH have not been investigated. We studied the prevalence of extracellular signal-regulated kinase (ERK) pathway mutations in different PLCH stages and other non-PLCH smoking-related lung diseases.
  
  
  RESULTS
  The cohort included 28 PLCH with cellular (n = 10), mixed cellular/fibrotic (n = 4) and fibrotic histology (n = 14). Seven cases had concurrent multi-focal/multi-lobar tumours. Respiratory bronchiolitis interstitial lung disease (RB-ILD, n = 2), desquamative interstitial pneumonia (DIP, n = 4) and mixed RB-ILD/DIP (n = 2) were included for comparison. BRAF(V) (600E) immunohistochemistry, next-generation sequencing (NGS) and peptide nucleic acid (PNA) clamp polymerase chain reaction (PCR) with high analytical sensitivity (<0.1-0.2%) were used to analyse RAS, BRAF and MAP2K1 genes. Of 26 cases with gene mutation data, BRAF(V) (600E) was identified in eight of 12 (67%) cellular cases and in one of 14 (7%) fibrotic cases. MAP2K1 or KRAS mutations were observed in four of 14 (29%) fibrotic cases and three of the 12 (25%) cellular cases. Multi-focal/multi-lobar specimens carried identical BRAF (n = 5) or non-hotspot MAP2K1 (n = 2) mutations. The other smoking-related disorders were negative for mutations. Patients with cellular lesions or BRAF mutation were significantly younger than patients with fibrotic or BRAF wild-type PLCH.
  
  
  CONCLUSIONS
  The presence of identical but mutually exclusive ERK pathway mutations in multi-focal PLCH supports a neoplastic/clonal origin for this disease. Patient age and mutation type differed between cellular and fibrotic histology and may indicate a natural progression or a mutation-specific pathogenicity.
authors.affiliation: Department of Pathology, Massachusetts General Hospital, Boston, MA, USA.
authors.forename: Michal
authors.initials: M
authors.lastname: Kamionek
authors.affiliation: Department of Pathology, University of Massachusetts Medical School, Worcester, MA, USA.
authors.forename: Parnian
authors.initials: P
authors.lastname: Ahmadi Moghaddam
authors.affiliation: Department of Pathology, University of Massachusetts Medical School, Worcester, MA, USA.
authors.forename: Ali
authors.initials: A
authors.lastname: Sakhdari
authors.affiliation: Department of Pathology, Massachusetts General Hospital, Boston, MA, USA.
authors.forename: Alexandra E
authors.initials: AE
authors.lastname: Kovach
authors.affiliation: Department of Pathology, University of Massachusetts Medical School, Worcester, MA, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Welch
authors.affiliation: Department of Pathology, University of Massachusetts Medical School, Worcester, MA, USA.
authors.forename: Xiuling
authors.initials: X
authors.lastname: Meng
authors.affiliation: Department of Pathology, University of Massachusetts Medical School, Worcester, MA, USA.
authors.forename: Karen
authors.initials: K
authors.lastname: Dresser
authors.affiliation: Department of Pathology, University of Massachusetts Medical School, Worcester, MA, USA.
authors.forename: Keith
authors.initials: K
authors.lastname: Tomaszewicz
authors.affiliation: Department of Pathology, University of Massachusetts Medical School, Worcester, MA, USA.
authors.forename: Ediz F
authors.initials: EF
authors.lastname: Cosar
authors.affiliation: Department of Pathology, Massachusetts General Hospital, Boston, MA, USA.
authors.forename: Eugene J
authors.initials: EJ
authors.lastname: Mark
authors.affiliation: Department of Pathology, University of Massachusetts Medical School, Worcester, MA, USA.
authors.forename: Armando E
authors.initials: AE
authors.lastname: Fraire
authors.affiliation: Department of Pathology, University of Massachusetts Medical School, Worcester, MA, USA.
authors.forename: Lloyd
authors.initials: L
authors.lastname: Hutchinson
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D004252:DNA Mutational Analysis; D005260:Female; D059014:High-Throughput Nucleotide Sequencing; D006646:Histiocytosis, Langerhans-Cell / Q000209:etiology / Q000235:genetics* / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D008171:Lung Diseases / Q000209:etiology / Q000235:genetics* / Q000473:pathology; D048369:MAP Kinase Kinase 1 / Q000235:genetics; D020935:MAP Kinase Signaling System / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D009154:Mutation; D016133:Polymerase Chain Reaction; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D012907:Smoking / Q000009:adverse effects; D055815:Young Adult; D018631:ras Proteins / Q000235:genetics
chemical_list: C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; D018631:ras Proteins
keywords: ERK pathway; PLCH; clonal neoplasm; natural history; pathogenesis