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 .PAX-5 is a member of the PAX (paired box) family of transcription factors involved in tissue and organ differentiation. PAX-5 (also known as B-cell activator protein) is a B-cell-specific transcription factor and expressed in the early pro-B, pre-B, and naïve stages of B-cell development until the mature B cells. It is expressed in B-cell lymphoma/leukemia,Reed-Sternberg cells of classic Hodgkin’slymphoma.