Syndecan-1 Expression on Malignant Cells from the Blood and Marrow of Patients with Plasma Cell Proliferative Disorders and B-Cell Chronic Lymphocytic Leukemia

Abstract

Syndecan-1 is a low-affinity receptor for basic fibroblast growth factor (bFGF). In this study, we used flow cytometry to examine expression of syndecan-1 on monoclonal cells from the blood (n = 37) and marrow (n = 81) of patients with plasma cell (PC) proliferative disorders (PCPD) and blood cells from patients (n = 39) with B cell chronic lymphocytic leukemia (B-CLL). The marrow CD38⁺CD45- and CD38⁺CD45⁺ PC were syndecan-1 positive in all patients with PCPD and there was no difference between patients with monoclonal gammopa-thy of undetermined significance (MGUS) vs multiple myeloma or cases with vs without bone lesions. In 38% of cases, syndecan-1 expression on the PC was heterogeneous with a25% of PC syndecan-1 negative. We found similar syndecan-1 expression on blood and marrow PC in the 36 cases with paired samples. CLL cells were syndecan-1 negative in 97% (38/39) of the cases. Syndecan-1 is a useful marker to detect malignant plasma cells in the blood or marrow; however, it is not helpful in distinguishing MGUS from active myeloma. In addition, syndecan-1 is present on the less mature (CD45⁺) PC, and there is heterogeneity of expression within and between patients. The relevance of the bFGF bound to myeloma cells via syndecan-1 remains to be elucidated.