title: Morphological and immunophenotypical features of hairy cell leukaemia involving lymph nodes and extranodal tissues.
abstract: OBJECTIVE
  Hairy cell leukaemia (HCL) is a rare B cell neoplasm that mainly affects bone marrow (BM), peripheral blood (PB) and spleen. Involvement of lymph nodes and extranodal structures is considered infrequent. Herein we describe our institutional experience of nodal (n = 10) and extranodal (n = 3) HCL during a 30-year period.
  
  
  RESULTS
  Ten patients had prior evidence of HCL within the BM or PB at a median 35.8 months before nodal/extranodal diagnosis (range: <1-175 months), and HCL was diagnosed concurrently within the bone marrow of one additional patient. Nodal involvement showed distinct architectural patterns, including diffuse (62% of cases), sinusoidal (25%) and nodular (13%). Extranodal involvement was characterized as diffuse infiltration through underlying structures in all cases. Morphological features ranged from classic 'fried-egg' cytology to a plasmacytoid appearance. Nodal/extranodal disease showed an overlapping immunophenotypical profile with other small B cell lymphomas, including expression of cyclin D1 (70%), CD43 (55%), CD10 (38%) and CD5 (8%). Rates of both CD43 and CD10 reactivity were higher than described previously in leukaemic HCL, suggesting that expression may be enriched in cases with extramedullary extension.
  
  
  CONCLUSIONS
  Although uncommon, HCL should be considered in the differential diagnosis of small B cell neoplasms involving nodal/extranodal sites, given the therapeutic implications. In particular, recent discoveries including detection of the BRAFV600Emutation in nearly all cases of HCL and the availability of an antibody to CD103 for use in paraffin-embedded tissues will facilitate the distinction of HCL from other small B cell lymphomas in the nodal/extranodal setting.
authors.affiliation: Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: Jacqueline M
authors.initials: JM
authors.lastname: Cortazar
authors.affiliation: Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, USA.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: DeAngelo
authors.affiliation: Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: Geraldine S
authors.initials: GS
authors.lastname: Pinkus
authors.affiliation: Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: Elizabeth A
authors.identifier: http://orcid.org/0000-0001-5880-9337
authors.initials: EA
authors.lastname: Morgan
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D014408:Biomarkers, Tumor / Q000032:analysis; D005260:Female; D006801:Humans; D016130:Immunophenotyping; D007943:Leukemia, Hairy Cell / Q000473:pathology*; D008198:Lymph Nodes / Q000473:pathology*; D008297:Male; D008875:Middle Aged
chemical_list: D014408:Biomarkers, Tumor
keywords: extranodal; hairy cell leukemia; lymph node