Test Details: Immunohistochemical testing is carried out on biopsy/resected tissue specimen. This testing helps to identify specific antigens (proteins) within tissue sections utilizing an antigen-specific antibody . CD138 (syndecan-1) is a transmembrane antigen and one of the four members of the syndecan family. The expression of CD138 is found in different maturation stages of B-lymphocytes and plasma cells and in different types of epithelial and mesenchymal cells. CD138 is widely used as a marker for plasma cells and plasma cell neoplasms.