Specificity: Recognizes a cell-cycle-associated protein of 345kD and 395kD identical with the human Ki-67 antigen. Binds to a formalin-resistant epitope of the Ki-67 antigen. Confined to the nuclei of proliferating cells and no cross-reactivity with cytoplasmic antigens of epithelial occurs even after antigen retrieval. Immunohistochemistry labeling of fresh and frozen samples showed identical results with Ki-67 and Ki-S5.