Retrospective Analysis of the Expression of CD56 in Multiple Myeloma with Bone-Related Extramedullary Diseases

To identify the clinical characteristics and tissue CD56 expression pattern in patients with multiple myeloma (MM) with bone-related extramedullary disease (b-EMD), not connected to or isolated from the bone marrow. We reviewed consecutive patients with MM hospitalised at the First Affiliated Hospital of Fujian Medical University between 2016 and 2019. Patients with b-EMD were identified, and the clinical and laboratory features of patients with and without b-EMD were compared. Immunohistochemistry of extramedullary lesions was performed based on b-EMD histology. Ninety-one patients were included in the study. Among them, 19 (20.9%) were found to have b-EMD at initial diagnosis. Median age was 61 years (range, 42-80 years), with a female/male ratio of 6/13. The most common site of b-EMD was the paravertebral space (11/19; 57.9%). Compared to those without b-EMD, patients with b-EMD had lower levels of serum β2-microglobulin and similar levels of lactate dehydrogenase. Immunophenotype analysis based on histopathology showed that CD56 was expressed in 9/10 (90.0%) patients with b-EMD. A considerable number of MM patients presented with b-EMD at the time of initial diagnosis, and most patients with b-EMD exhibited CD56 expression, highlighting a potential new therapeutic target in the future.