title: Grading of follicular lymphoma: comparison of routine histology with immunohistochemistry.
abstract: BACKGROUND
  Follicular lymphoma (FL) grading is based on the average number of large transformed cells in 10 neoplastic follicles at x40 high-power field (x10-40 high-power field) examination (grade 1, 0-5 centroblasts per high-power field; grade 2, 6-15 centroblasts per high-power field; grade 3, >15 centroblasts per high-power field).
  
  
  OBJECTIVE
  Since there may be significant interobserver variability, we analyzed the usefulness of immunohistochemical stains in grading FLs more reliably.
  
  
  METHODS
  Forty-three FLs initially graded by World Health Organization criteria (grade 1, 12; grade 2, 18; grade 3, 13) were reviewed and stained with CD3, CD20, Ki-67, CD30, CD68, PAX-5, and BCL-6. Retrospective review was performed for the average number of large cells, of large lymphoid cells, of large cells staining with CD3, CD20, BCL-6 (40 cases), and PAX-5, and of all cells staining with CD68, Ki-67, and CD30.
  
  
  RESULTS
  By histologic review, 8 of 43 FLs had a significant grade change (4 cases upgraded and 4 cases downgraded). CD3 and CD30 stained only 0 to 3 large cells and 0 to 3 cells, respectively, in neoplastic follicles. CD68+ cells represented the large nonlymphoid cells. Increasing FL grades demonstrated increases in Ki-67+ cells. The original grade showed substantial agreement with CD20 and moderate agreement with PAX-5 and BCL-6. The original histologic grade agreed with immunohistochemical-based grade using 2 or more antibodies in 5 of 8 discordant cases (4 by CD20 or BCL-6 and PAX-5; 1 by CD20, PAX-5, and BCL-6).
  
  
  CONCLUSIONS
  Interobserver variability of histologic FL grading may be significant; we showed low-end "substantial agreement." Immunohistochemical stains (ie, CD20, PAX-5, and BCL-6) may more reliably determine the number of large transformed cells in neoplastic follicles; Ki-67 staining correlates with higher FL grades. Immunohistochemical stains may be evaluated in clinical trials of FL patients to determine prognostic significance.
authors.affiliation: Division of Hematopathology, Department of Pathology and Laboratory Medicine, Lineberger Cancer Center, University of North Carolina, Chapel Hill, NC 27599-7525, USA.
authors.forename: Antonio E
authors.initials: AE
authors.lastname: Martinez
authors.forename: Li
authors.initials: L
authors.lastname: Lin
authors.forename: Cherie H
authors.initials: CH
authors.lastname: Dunphy
mesh_terms: D015703:Antigens, CD; D018951:Antigens, CD20 / Q000032:analysis; D015214:Antigens, Differentiation, Myelomonocytic; D017252:CD3 Complex / Q000032:analysis; D004268:DNA-Binding Proteins / Q000032:analysis; D006801:Humans; D007150:Immunohistochemistry; D017730:Ki-1 Antigen / Q000032:analysis; D019394:Ki-67 Antigen / Q000032:analysis; D008224:Lymphoma, Follicular / Q000737:chemistry / Q000473:pathology*; D051757:PAX5 Transcription Factor / Q000032:analysis; D051560:Proto-Oncogene Proteins c-bcl-6; D000097382:CD68 Molecule
chemical_list: D015703:Antigens, CD; D018951:Antigens, CD20; D015214:Antigens, Differentiation, Myelomonocytic; D017252:CD3 Complex; D004268:DNA-Binding Proteins; D017730:Ki-1 Antigen; D019394:Ki-67 Antigen; D051757:PAX5 Transcription Factor; D051560:Proto-Oncogene Proteins c-bcl-6; C084103:BCL6 protein, human; C067980:CD68 antigen, human; D000097382:CD68 Molecule; C497281:PAX5 protein, human