Oncoprotein coexpression in human aberrant crypt foci and minute polypoid lesions of the large bowel

Background: Genetic aberrations observed in the large bowel during the neop lastic progression have a cumulative effect and are responsible for the pro pagation of the multistep malignant process. In the present study we evalua ted the immunoreactivity of c-fos, ras, bcl-2 and p53 in aberrant crypt foc i (ACF) and minute polyps of the large bowel obtained from patients with co lorectal cancer. Methods: ACF and minute polyps were collected from macrosc opically normal colonic mucosa. Protein immunoreactivity was detected on pa rafin sections utilizing the biotinstreptavidin method on 25 hyperplastic, 10 dysplastic ACF, 5 hyperplastic and 10 dysplastic adenomas. Results: 41% of the lesions displayed positive ras immunoreactivity. bcl-2 immunoreactiv ity was positive in six minute polyps of which five were neoplastic. fos im munoreactivity was detected in 5 ACF and seven minute polyps, mainly in dys plastic lesions. Two neoplastic polyps were positive for p53 immunoreactivi ty. Coexpression of two or more oncoproteins was found with increasing freq uency in dysplastic versus hyperplastic lesions and in polypoid lesions ver sus ACF. Conclusions: Abnormal expression and coexpression in oncoproteins can be identified in the earliest stages of colorectal tumorigenesis and ma y contribute to the progression of selected lesions during ACF-adenoma-carc inoma sequence.