title: Leukocyte common antigen (CD45) negative follicular lymphoma, a rare immunophenotypic presentation.
abstract: BACKGROUND
  CD45 is universally expressed on nucleated hematopoietic cells in healthy individuals with variable intensities. Although down-regulation of CD45 expression is commonly seen in immature B-cell neoplasm, loss of CD45 expression is rarely observed in mature B-cell lymphoproliferative disorders.
  
  
  METHODS
  A 64-y old man was presented with fatigue and night sweat in July 2013. Physical examination revealed right axillary lymphadenopathy without splenohepatomegaly. The lymph node was sent for flow cytometry and histomorphologic evaluation. Flow cytometric analysis revealed the presence of CD45+ and CD45- cell populations. The CD45+ population (42%) comprised mainly unremarkable CD3+ T cells. However, the CD45- population (35%) showed CD19+, CD20+, and CD10+ immunophenotype with monotypic surface Lambda immunoglobulin light chain expression. Immunohistochemical studies performed on tissue section revealed that neoplastic lymphoid nodules were positive for CD20, BCL-6 and BCL-2 with low proliferation index by Ki-67 staining, but again negative for CD45. FISH analysis confirmed the presence of IGH/BCL2 rearrangement. Follicular lymphoma (grade 1) with negative CD45 expression was diagnosed.
  
  
  CONCLUSIONS
  Loss of CD45 expression has been reported, but all cases documented were large B cell lymphoma (LBCL). To the best of our knowledge, this is the first case of low grade follicular lymphoma with lack of CD45 expression. We report this case because of not only its rarity but also to raise awareness that loss of CD45 expression can occur in LBCL as well as in low grade B-cell lymphomas.
authors.affiliation: Department of Clinical Laboratory, Peking Union Medical College Hospital, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing, China.
authors.forename: Fei
authors.initials: F
authors.lastname: Wang
authors.affiliation: Department of Hematopathology, CBLPath, Inc., Rye Brook, NY, United States.
authors.forename: Dongsheng
authors.initials: D
authors.lastname: Xu
authors.affiliation: Department of Clinical Laboratory, Peking Union Medical College Hospital, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing, China. Electronic address: cuiw@pumch.cn.
authors.forename: Wei
authors.initials: W
authors.lastname: Cui
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D016130:Immunophenotyping; D017493:Leukocyte Common Antigens / Q000378:metabolism*; D008224:Lymphoma, Follicular / Q000175:diagnosis / Q000276:immunology* / Q000378:metabolism* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D060787:Neoplasm Grading
chemical_list: D017493:Leukocyte Common Antigens
keywords: CD45; Flow cytometry; Follicular lymphoma