Most antibodies used in IHC assays were developed for use with formalin-fixed tissue and include steps for unmasking epitopes. When working with PAXgene Tissue treated specimens, test for each antibody to determine if it is necessary to perform antigen-retrieval steps. In addition, it may be necessary to optimize antigen-retrieval steps or adjust antibody concentrations in PFPE tissue to achieve optimal staining intensities (see Technical Note Effect of epitope retrieval conditions on immunohistochemical staining of PFPE tonsil tissue with anti-human Ki-67 antigen (clone MIB-1) under the Product Resources tab). Examples for IHC staining of adjacent human tissue sections fixed with neutral-buffered formalin or with PAXgene Tissue reagents are provided in the Tissue Atlas at www.preanalytix.com.