title: Activation-induced cytidine deaminase expression in diffuse large B-cell lymphoma with a paracortical growth pattern: a lymphoma of possible interfollicular large B-cell origin.
abstract: BACKGROUND
  Activation-induced cytidine deaminase, necessary for immunoglobulin somatic hypermutation and class switch recombination, is usually expressed within the follicular dendritic network but is also expressed in a population of interfollicular large B cells outside the germinal center.
  
  
  OBJECTIVE
  To report 7 cases of diffuse large B-cell lymphoma with a distinct paracortical distribution. Expression of activation-induced cytidine deaminase, previously described in interfollicular large B cells, was evaluated.
  
  
  METHODS
  A panel of immunohistochemical markers, including double staining for activation-induced cytidine deaminase and CD20, was used to illustrate the cases. Molecular studies were performed by polymerase chain reaction in the paraffin-embedded tissue for t(14;18) chromosomal translocation and immunoglobulin heavy chain and T-cell receptor rearrangements.
  
  
  RESULTS
  Patients included 3 males and 4 females ranging in age from 11 to 59 years (mean, 39 years). All specimens were lymph nodes (4 from the groin, 2 from the neck, and 1 from the axilla). Malignant lymphocytes were positive for CD20 and negative for CD5 and CD10. Staining for CD30, CD43, and BCL-2 was variable. The malignant cells showed at least focal staining with activation-induced cytidine deaminase. All cases were found to be monoclonal by immunoglobulin heavy-chain gene rearrangement or showed light-chain restriction. None of the tested cases showed t(14;18).
  
  
  CONCLUSIONS
  Diffuse large B-cell lymphoma with a paracortical distribution is unusual and may be a distinct morphologic variant. More study is necessary to determine the stage of B-cell development and the cell of origin of these tumors. However, activation-induced cytidine deaminase expression suggests they may arise from a putative interfollicular large B cell.
authors.affiliation: Department of Hematopathology, Armed Forces Institute of Pathology, Washington, DC 20306-6000, USA. aguilera@afip.osd.mil
authors.forename: Nadine S
authors.initials: NS
authors.lastname: Aguilera
authors.forename: Aaron
authors.initials: A
authors.lastname: Auerbach
authors.forename: Carol L
authors.initials: CL
authors.lastname: Barekman
authors.forename: Jack
authors.initials: J
authors.lastname: Lichy
authors.forename: Susan L
authors.initials: SL
authors.lastname: Abbondanzo
mesh_terms: D000293:Adolescent; D000328:Adult; D018951:Antigens, CD20 / Q000378:metabolism; D014408:Biomarkers, Tumor / Q000378:metabolism; D002648:Child; D002999:Clone Cells; D003564:Cytidine Deaminase / Q000096:biosynthesis* / Q000235:genetics; D004789:Enzyme Activation; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D008198:Lymph Nodes / Q000473:pathology; D008224:Lymphoma, Follicular / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D016403:Lymphoma, Large B-Cell, Diffuse / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D008297:Male; D008875:Middle Aged; D055815:Young Adult
chemical_list: D018951:Antigens, CD20; D014408:Biomarkers, Tumor; D003564:Cytidine Deaminase