Immunohistochemical staining pattern of lymphoma with the horseradish peroxidase–labelled Ki-67 antibody MIB-1 and Bcl-2 antibody Bcl2/100, showing their reactivity in mantle cell lymphoma and diffuse large B-cell lymphoma. Cells were stained with 3,3'-diaminobenzidine for detection of Ki-67 and Bcl-2 expression (brown staining) and with hematoxylin for visualization of nuclei (blue staining). (A) In this mantle cell lymphoma, Ki-67 is weakly expressed, whereas strong expression of Bcl-2 is observed. However, these markers are known to be differentially expressed in mantle cell lymphoma. (B) Strong Ki- 67 and Bcl-2 expression is observed in the presented diffuse large B-cell lymphoma. These markers are primarily used for subtyping this group of malignancies. Provided by Ruud Clarijs, Department of Pathology, Zuyderland Medical Centre (magnification ×400).