Methodological aspects of using immunohistochemical cell proliferation biomarkers in colorectal carcinoma chemoprevention.

In vitro uptake of bromodeoxyuridine (BrdU), expression of proliferating cell nuclear antigen (PCNA), and expression of antigen Ki-67 as revealed by the MIB-1 antibody in fixed and embedded tissues have been regarded as markers of cell proliferation in colorectal tumor progression. Proliferation distribution abnormalities in high-risk mucosa have been illustrated in detail by BrdU labeling of cells in S phase, whereas PCNA and MIB-1 are less informative at this stage of carcinogenesis. The reliability of BrdU labeling is, in any event, dependent on optimization of its tissue uptake and diffusion. Neoplastic deregulation of the synthesis and expression of PCNA, coupled with striking variations in nuclear immunostaining intensity, imposes caution on its use as an intermediate biomarker in intestinal chemoprevention. Validation of MIB-1 must await the standardization of some of the critical procedures (e.g., treatment with microwaves) of antigen retrieval.