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. CD79a exhibits a membranous stain, but plasma cells may also show a cytoplasmic staining pattern. The expression of CD79a is independent of the expression of CD20 and remains positive after the anti-CD20 immunotherapy. CD79a is used for the diagnosis of B-cell lymphoma, but is positive in a small fraction of T-ALL, AML.