title: Modulation of CD20 antigen expression after rituximab treatment: a retrospective study in patients with chronic lymphocytic leukemia.
abstract: BACKGROUND
  CD20 antigen down-modulation by anti-CD20 rituximab treatment is a well-recognized phenomenon in patients with non-Hodgkin's lymphoma. However, few data are currently available on this topic in other lymphoproliferative disorders, in particular in chronic lymphocytic leukemia (CLL).
  
  
  OBJECTIVE
  The aim of this study was to establish how many patients with CLL show a disappearance of CD20 antigen after salvage treatment with rituximab and its possible clinical significance.
  
  
  METHODS
  We sequentially analyzed CD20 expression by flow cytometry in patients treated with rituximab in combination with other agents for relapsed/resistant disease.
  
  
  RESULTS
  Eleven white patients with CLL (6 females, 5 males; median age, 71.6 years [range, 60-84 years]) were included in the study. Three of the 11 patients were not positive for CD20 due to complete response at baseline. Four of the remaining 8 patients (50%) lacked CD20 antigen on neoplastic cells after monoclonal antibody treatment. Two of them developed Richter's syndrome and died within 4 months. The phenomenon was transient in the other 2 patients, who were alive after a follow-up of 25 and 26 months, respectively, with CD20-positive recurrent disease.
  
  
  CONCLUSIONS
  In this study, CD20 antigen disappearance in patients with CLL treated with rituximab-containing salvage regimens occurred in 4 of 8 (50%) tested patients, half of whom developed Richter's syndrome. [Note: Since the initial writing and submission, a third patient developed Richter's syndrome.] In 2 patients (50%), CD20 returned at progression.
authors.forename: Fiorella
authors.initials: F
authors.lastname: D'Auria
authors.forename: Roberto
authors.initials: R
authors.lastname: Guariglia
authors.forename: Oreste
authors.initials: O
authors.lastname: Villani
authors.forename: Giovanna
authors.initials: G
authors.lastname: Mansueto
authors.forename: Vitina
authors.initials: V
authors.lastname: Grieco
authors.forename: Antonia
authors.initials: A
authors.lastname: Zonno
authors.forename: Gabriella
authors.initials: G
authors.lastname: Bianchino
authors.forename: Luigina
authors.initials: L
authors.lastname: Di Giovannantonio
authors.forename: Giulia
authors.initials: G
authors.lastname: Vita
authors.forename: Pellegrino
authors.initials: P
authors.lastname: Musto
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D058846:Antibodies, Monoclonal, Murine-Derived / Q000494:pharmacology*; D018951:Antigens, CD20 / Q000187:drug effects* / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology*; D005260:Female; D005434:Flow Cytometry; D005500:Follow-Up Studies; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000188:drug therapy* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D012008:Recurrence; D012189:Retrospective Studies; D000069283:Rituximab; D016879:Salvage Therapy / Q000379:methods; D016896:Treatment Outcome
chemical_list: D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20; D000970:Antineoplastic Agents; D000069283:Rituximab