Abstract

Prognostic factors available to help predict the outcome of patients with B-cell chronic lymphocytic leukemia (B-CLL) include clinical stage, lymphocyte doubling time, cytogenetic abnormalities, immunoglobulin heavy chain variable region (IgVH) mutation status, serum factors such as soluble CD23 and, in particular, cellular phenotyping. For instance, several studies have shown that cellular expression of CD38 or zap-70, as assessed by flow cytometry, is associated with a more aggressive course of disease. However, previous phenotyping studies have not addressed the significance of more subtle findings such as whether bimodal expression (the identification of two discrete cell populations within the neoplasm) or the level of antigen expression impacts patient outcome. Therefore, a retrospective analysis of flow cytometry data from 246 patients diagnosed with B-CLL at University Hospitals of Cleveland and Case Western Reserve University was performed. Twenty-five different antigens were assessed for bimodality and the level of expression of all antigens was determined on a 0–3 scale. CD38 and CD71 expression level was further analyzed as percent positive over control. The optimal threshold values of CD38 and CD71 was estimated by the tree-structure survival method. Bimodality was identified by visual inspection of the flow cytometry histograms. The overall survival was measured from the date of analysis to date of death and censored at the date of last follow-up for survivors. Survival distribution was estimated using Kaplan-Meier methods and difference between/among groups was examined using log rank test. The mean follow-up was an average of 2.7 years. Bimodal antigen expression was found in 107 (43%) of all analyzed cases. However, neither the presence of bimodality by itself, nor the number of bimodal antigens per case was associated with worse overall survival. Bimodality of CD38, identified in 14.5% of cases, was not correlated with a worse overall survival in this study and bimodality of individual antigens CD13 (12.9%), CD11c (7.9%), CD20 (7.3%), CD5 (7.3%), FMC-7 (6.4%), and surface immunoglobulin (4.5%) also did not impact survival. Antigens bimodal in less than 4.5% of cases were not analyzed. In multivariate analysis, the expression level of CD38, CD23 and CD71 were found to be independent prognostic risk factors. The effect of CD38, CD23, and CD71 on overall survival, controlling for the effect of age, was further estimated using the Cox proportional hazards model. The relative risk of dying for patients with CD71 expression on B-CLL cells less than 9.5% was 6.37 (p = 0.0001, CI 2.56–15.87) compared to patients expressing higher levels of CD71. Patients with low level B-CLL cellular CD23 expression had a relative risk of dying of 4.22 (p= 0.007, CI 1.49–11.9) compared to those patients expressing higher levels of CD23 and those patients with B-CLL cells expressing CD38 greater than 24.5% had a relative risk of dying of 2.85 (p = 0.016, CI 1.22 – 6.65) compared to those patients expressing lower levels of CD38. Taken together, our findings show for the first time that cellular expression of CD23 and CD71 impact survival in B-CLL and indicate that the level of expression of CD38, CD23, and CD71 are independent risk factors while bimodal antigen expression appears not to influence outcome in B-CLL patients.

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