CD138 + Ki-67

CD138/syndecan-1 is an excellent marker for identifying plasma cells, as CD138 is a transmembrane heparin proteoglycan present on the surface membrane of plasma cells that remains active in formalin-fixed paraffin-embedded bone marrow sections. Other hematopoietic cells, endothelial cells and lymphoplasmacytoid lymphomas in bone marrow are CD138 negative (1). CD138 is also expressed in fibroblasts, keratinocytes and normal hepatocytes (1).

The Ki-67 antibody identifies a nuclear antigen, which is associated with cell proliferation. It is found throughout the cell cycle in the G1, S, G2, and M phases; but not in the GO phase. It is commonly used to grade the proliferation index of tumors (2).

As CD138 is localized to the cell membrane, it can be paired with nuclear prognostic markers, such as Ki-67, in double-marker immunostaining reactions without overlap of the chromogenic signals. In multiple myeloma, a CD138 + Ki-67 IHC double stain was shown to be more sensitive and accurate for myeloma cell proliferation assessment than cytogenetic methods (3).