title: The immunophenotypic stability of plasma cell myeloma by flow cytometry.
abstract: BACKGROUND
  Flow cytometry (FC) has become increasingly utilized in the diagnosis and monitoring of plasma cell myeloma (PCM), though few studies have evaluated the longitudinal stability of antigen expression.
  
  
  METHODS
  We studied 45 PCM patients by four-color FC for shifts in CD19, CD20, CD38, CD45, CD56, and cytoplasmic light chain expression, between diagnostic/first encounter and positive follow-up analyses. An immunophenotypic (IP) change was defined as gain, loss, or ½ log shift of antigen expression.
  
  
  RESULTS
  An IP change was observed in 14/45 (31%) patients, with single IP changes in 9/14, two changes in 2/14, and three changes in 3/14. 3/14 reverted from an aberrant to a normal plasma cell IP, while remaining light chain-restricted. Changes in expression of CD45 occurred in 9/45 (20%), CD19 in 5/45 (11.1%), CD20 in 2/45 (4.4%), and CD56 in 5/45 (11.1%).
  
  
  CONCLUSIONS
  Approximately 1/3 of PCM cases show IP changes over time, with CD45 the least stable antigen. Recognition of this relative instability is important to avoid narrow targeting of follow-up FC analyses, especially for minimal residual disease monitoring.
authors.affiliation: Department of Pathology, Medical College of Wisconsin, Milwaukee, WI, USA.
authors.forename: M D
authors.initials: MD
authors.lastname: Spears
authors.forename: H
authors.initials: H
authors.lastname: Olteanu
authors.forename: S H
authors.initials: SH
authors.lastname: Kroft
authors.forename: A M
authors.initials: AM
authors.lastname: Harrington
mesh_terms: D000328:Adult; D000368:Aged; D001854:Bone Marrow Cells / Q000378:metabolism / Q000473:pathology; D005260:Female; D005434:Flow Cytometry; D005500:Follow-Up Studies; D006801:Humans; D016130:Immunophenotyping; D008297:Male; D008875:Middle Aged; D009101:Multiple Myeloma / Q000175:diagnosis* / Q000378:metabolism*; D010950:Plasma Cells / Q000378:metabolism* / Q000473:pathology