Bcl-6 is a Kruppel-type zinc finger transcription factor spanning 706 amino acids. Bcl-6 plays a central role in germinal center (GC) formation, functioning as a regulator of B lymphocyte growth and development by protecting GC B cells from undergoing DNA damage-induced apotosis. Logarajah S et al. found that Bcl-6 is involved in mammary epithelial differentiation, which may play a potential role in carcinogenesis. Bcl-6 expression is mainly localized in GC B cells. Surrounding mantle- and marginal-zone B cells, as well as plasma cells and marrow B-cell precursors are negative for Bcl-6. Bcl-6 protein is commonly detected in GC neoplasms including follicular lymphomas, diffuse large B-cell lymphoma (DLBCL) and Burkitt's lymphomas. Bcl-6 is not restricted to B-cell lineage, a considerable number of anaplastic large cell lymphoma also had Bcl-6 expression, especially in ALK positive cases.