Aberrant crypt foci (ACF) are clusters of abnormal tube-like glands in the lining of the colon and rectum.
Aberrant crypt foci form before colorectal polyps and are one of the earliest changes seen in the colon that may lead to cancer.
When looking for aberrant crypt foci with microscopy, methylene blue is used as a staining agent.
[1] The resulting figure is fairly easy to detect under the microscope at low magnification (x40).
[5] Resveratrol glucoside from transgenic alfalfa has been used for the prevention of aberrant crypt foci in mice.