FMC7 antigen expression on normal and malignant B‐cells can be predicted by expression of CD20

Most antibody panels proposed for flow cytometric immunophenotyping of non‐Hodgkin's lymphomas and chronic lymphoid leukemias include anti‐CD20 and FMC7 antibodies. As in our experience, reactivity of B‐cells with these antibodies seemed to be correlated, we evaluated whether the simultaneous use of anti‐CD20 and FMC7 antibodies is justified. Using flow cytometry, we measured the binding of these 2 antibodies to the B‐cells of 67 bone marrow aspirates, 31 lymph node biopsies, 18 peripheral blood specimens, and 12 tissue samples from other locations. The diagnoses included 50 cases without overt abnormalities, 5 reactive lymphadenopathies, 56 lymphomas and chronic lymphoid neoplasias, and 17 cases with other malignancies. Although CD20 expression was consistently higher, we observed a significant and strong correlation between CD20 and FMC7 antigen expression on B‐lymphocytes, irrespective of the nature of the sample or disease (r = 0.910; P < 0.001). Moreover, FMC7 antigen expression on B‐cells could be predicted by CD20 expression with a sensitivity of 96%, a specificity of 94% and an efficiency of 96%. Our results show that although differing in intensity, expression of CD20 on B‐cells closely parallels that of FMC7 antigen. We, therefore, conclude that little additional information is revealed by using FMC7 in immunophenotyping of non‐Hodgkin's lymphomas or chronic lymphoid leukemias if intensity of CD20 expression is taken into consideration. Cytometry (Comm. Clin. Cytometry) 34:71–74, 1998. © 1998 Wiley‐Liss, Inc.