Diagnostic Significance of CD20 and FMC7 Expression in B-Cell Disorders

Abstract

We analyzed by flow cytometry the expression of CD20 and FMC7 in cell suspensions
\nfrom 932 patients, including 630 cases of chronic lymphocytic leukemia (CLL), 23 
\ncases of other B-cell leukemias, and 279 cases of B-cell non-Hodgkin lymphoma
\n(B-cell NHL). CD20 was positive in 94.5% of cases; FMC7 was positive in 35.7%.
\nThere was a correlation between CD20 and FMC7 expression in patients with B-cell 
\nNHL (P < .001) but not CLL (P = .1). We also tested a scoring system in which
\nFMC7 was replaced by CD20 and compared it with our current scoring system for
\nCLL. With this modification, the accuracy of the scoring system for
\ndifferentiating CLL from other non-CLL disorders fell from 94.4% to 81.5%. In
\nCD20+ CLL, the intensity of CD20 expression correlated with FMC7 and low scores
\n(P < .001 for both comparisons). We suggest that the particular conformation of
\nCD20 recognized by FMC7 is manifested only in cells with strong CD20 expression, 
\nwhich is not the case for CLL. FMC7 is of greater diagnostic value than CD20 for 
\ndistinguishing CLL from other B-cell disorders; we recommend its continued use
\nfor this purpose.