| Marker | Expression | Significance |
|---|---|---|
| CD138 (Syndecan-1) | Positive | Plasma cell marker; nearly universal in MM |
| CD38 | Positive | Activation marker; prognostic significance |
| CD19 | Negative | B-cell marker; lost during plasma cell differentiation |
| CD45 | Negative | Pan-leukocyte marker; absent in mature plasma cells |
| CD20 | Negative | B-cell marker; typically lost in myeloma |
| CD27 | Variable | May be present or absent |
| CD56 | Positive (70%) | NK cell marker; aberrantly expressed |
During normal B-cell to plasma cell differentiation, cells progressively lose B-cell associated antigens (CD19, CD20) while gaining plasma cell markers (CD138, CD38). In myeloma, this differentiation is arrested at the malignant plasma cell stage, resulting in the characteristic CD19−, CD20−, CD38+, CD138+ phenotype.
CD38 expression has prognostic significance—CD38+ myelomas may have different treatment responses compared to CD38− cases. Additionally, CD38 is a therapeutic target for monoclonal antibodies like daratumumab.
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