Background. Rituximab is being used successfully in the treatment of patients with chronic B-cell lymphoproliferative diseases. The success of treatment by rituximab is influenced, among other factors, by the antigen density on tumor cells. Therefore, the authors analyzed and compared the densities of the CD20 antigen in patients with chronic lymphoproliferative diseases. Methods and Results. Previously untreated patients with B-chronic lymphocytic leukemia (B-CLL), mantle-cell lymphoma (MCL), and small-cell lymphocytic lymphoma (SCLL) were evaluated by flow cytometry. The control group consisted of blood donors. The CD20 density was measured on tumor cell populations in patients and on the B-lymphocytes of the control group. The density was expressed in MESF. In the patients with B-CLL and SCLL, the CD20 density was low (25 300 vs. 36 100 MESF) and it was significantly lower than in donors (172 800 MESF; p<0.001). The difference between B-CLL and SCLL patients was not statistically significant. The density in MCL patients (196 300 MESF) was comparable to that of donors. Conclusions. We did not prove statistical different density of CD20 antigen in patients with SCLL when compared with B-CLL patients. High density in MCL patients may be helpful in differential diagnosis against B-CLL and SCLL.

        Key words: rituximab, flow cytometry, density, CD20, chronic lymphocytic leukemia, small cell lymphocytic lymphoma, mantle cell lymphoma.