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Immunohistological p53 staining is of limited value in the staging and prognostic prediction of colorectal cancer.

PURPOSE
To compare immunohistochemical staining using different anti-p53 antibodies, and to evaluate the possible clinical implications of the overexpression of p53 in a series of patients resected for colorectal cancer with a long follow-up.


METHODS
Tumor biopsy samples were collected from 294 surgical colorectal cancer specimens, obtained from two series of patients with a median follow-up of 4.5 years. The samples stained with four commercially available anti-p53 antibodies, (mouse monoclonal antibodies 421, 1801, and DO-7; and rabbit polyclonal antibody CM1), were evaluated and compared with cryosections from a subset of 20 biopsies from tumors in various stages and grades, obtained from patients with different outcomes.


RESULTS
DO-7 gave a homogeneous nuclear staining, which, when further investigated, turned out to be identical in the formalin-fixed paraffin-embedded and in the frozen specimens. Therefore, DO-7 was found to be suitable for the further analysis of archival or frozen sections from the sample. p53 overexpression was shown in 162 (55%) cases, with a significantly higher proportion having DNA aneuploidy (p<0.01) in left-sided colonic and rectal tumors (p<0.01). p53 staining was not associated with tumor stage, tumor grade, or survival.


CONCLUSIONS
A significantly higher proportion of p53 overexpressing tumors are DNA aneuploid, indicating that mutations in the TP53 gene constitute a sign of genetic instability, which might be of importance in malignant transformation. However, we could not find any indication that TP53 mutations, as reflected in the overexpression of p53, constitute a prerequisite for tumor progression in colorectal cancer.