The diagnostic utility and frequency of CD56 expression in plasma cell myeloma

Plasma cell myeloma (PCM) is a hematological malignancy characterized by systemic proliferation of neoplastic plasma cells within the bone marrow. Diagnosis requires clinical findings and immunohistochemical staining, including CD138, CD79a, cyclin D1, immunoglobulin κ (Igκ), and λ (Igλ). However, CD79a and cyclin D1 have limited sensitivity and specificity, and Igκ/Igλ assessment is often difficult due to overstaining. Therefore, more reliable antibodies are needed to accurately diagnose PCM. In this study, we examined the diagnostic utility of CD56 expression in PCM. We retrospectively performed immunostaining for CD138, CD56, CD79a, cyclin D1, Igκ, and Igλ in bone marrow samples from 116 patients with PCM. CD56 expression was observed in 85/116 cases (73.3 %), CD79a was downregulated in 46/116 cases (39.7 %), and cyclin D1 expression was observed in 42/116 cases (36.2 %). The expression of CD56 was significantly higher than that of CD79a and cyclin D1 (both p < 0.001). The combination of two antibodies resulted in the highest detection rate when combining CD56 and CD79a (105/116, 90.5 %), which was significantly higher than the detection rates of CD56 and cyclin D1 (93/116, 80.2 %) and CD79a and cyclin D1 (75/116, 64.7 %) (both p < 0.001). In contrast, lymphoplasmacytic lymphoma and marginal zone lymphoma lacked CD56 and cyclin D1 expression. Furthermore, in cases where light chain restriction was undetectable (11/116, 9.5 %), all could be diagnosed as PCM based on CD56, CD79a, and cyclin D1. Among these, CD56 showed the highest detection rate (8/11, 72.7 %). These findings highlight CD56 as a helpful marker for PCM diagnosis and support further clinical research.