The cover image shows an aberrant crypt foci (ACF) from formalin-fixed, paraffin-embedded rectal mucosa at 40X magnification. The lesion was identified and biopsied during colonoscopy. Immunohistochemistry for Ki-67, a proliferation marker, was performed on serial 4-5 μm sections of the tissue. Ki-67 protein is located in the nucleus of cells that are in S-phase of the cell cycle. Nuclei of negative cells show the blue counter-stain, hematoxylin. In normal colon, proliferating enterocytes are restricted to the bottom third of the crypts. The ACF demonstrated was hyperproliferative since the number of positively stained nuclei in enterocytes was greater than matching normal controls. See article by Cho et al. on page 21 for more information. Image courtesy of Adelaide M. Carothers.

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