CD13 Expression in B-Cell Chronic Lymphocytic Leukemia is Associated with the Pattern of Bone Marrow Infiltration

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Abstract
The ectopic expression of the cell surface peptidase CD13 (aminopeptidase N) and of three other myelomonocytic antigens i.e. CD33, CD14 and CD15 was analyzed by flow cytometry in neoplastic lymphocytes from 81 consecutive patients with B-cell chronic lymphocytic leukemia (B-CLL). CD13 and CD14 antigens were detected on lymphocytes from 30% and 60% of patients respectively whilst a smaller percentage of samples was found positive for CD15 (5%) and CD33 (12%). The presence of CD13 and CD33 antigens on neoplastic B cells showed a statistically significant association with the two most important clinicopathologic prognostic factors in B-CLL: the clinical stage (CD13, p < 0.01; CD33, p < 0.05—Rai and Binet staging systems) and the pattern of bone marrow infiltration (CD13, p < 0.001; CD33, p = 0.02). A multiple logistic regression analysis showed that the increased risk of CD13 positive patients (13.7 fold higher than in CD13 negative cases; p = 0.001) of presenting a diffuse pattern of bone marrow infiltration was independent from all other prognostic factors including sex, lymphocyte counts, age, and clinical stage. Our findings indicate for the first time a statistically significant association of CD13 and CD33 antigens with unfavorable prognostic factors in B-CLL. They suggest that the cross-lineage expression of myeloid-associated surface peptidases (CD13) and/or molecules related to cell adhesion processes (CD33), may influence the behaviour of B-cell chronic lymphoproliferative disorders in analogy to what is reported for acute leukemias and multiple myeloma.