Clinical and laboratory significance of CD56 (a neural cell adhesion molecule) positivity in multiple myeloma and AL amyloidosis

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CD56 is frequently expressed by malignant plasma cells in patients with multiple myeloma (MM) or AL amyloidosis (ALA). The aim of this retrospective study was to examine CD56 expression in patients with MM or ALA and determine the clinical and laboratory characteristics associated with its expression. Bone marrow samples of patients were analyzed by flow cytometry. Various clinical data with regard to the expression or non-expression of CD56 were compared. In total, 316 patients (215 with MM and 101 with ALA) were included in the study. The CD56 expression rate was higher in patients with MM than that in those with ALA. Patients with MM had a median CD56 expression rate of 96.4%, and serum total protein levels were significantly higher in the CD56+ group (p < 0.001). Patients with ALA had a median CD56 expression rate of 1.9%, and serum lactate dehydrogenase levels were significantly higher in the CD56+ group (p = 0.033). These findings suggest that the CD56 expression rate differs in monoclonal plasma cells between patients with MM and ALA, and that M-protein secretions are increased in patients with CD56+ MM.