The expression of the nuclear
phosphoprotein p53 was studied immunohistochemically in a series of 150 benign and malignant
colorectal tumors. Using
monoclonal antibody PAb1801,
tumors divided unequivocally into two groups on the basis of immunohistochemistry. Forty of the
carcinomas (46.5%) showed positive staining but only 4 of the
adenomas (8.7%) were positive (P less than 0.001). The few positive
adenomas always showed moderate or severe dysplasia. Metaplastic
polyps (n = 9) and small
familial adenomatous polyposis-related
adenomas (n = 9) were uniformly negative.
Carcinomas with p53 expression did not differ from those without in terms of site, differentiation or the prognostic indicators of Dukes' stage,
DNA ploidy, or
tumor histology. The improved morphologic resolution available in
periodate lysine paraformaldehyde dichromate (PLPD)-fixed,
paraffin-embedded tissue permitted several conclusions to be made: p53 is confined to neoplastic nuclei; staining in positive
tumors is heterogeneous and often more marked at the infiltrative margins; and staining intensity is dramatically reduced in mitotic cells. It is concluded that expression of immunohistochemically detectable p53 (probably representing mutated forms of the
protein) occurs in some
adenomas around the time of transition to
carcinoma. Therefore there is an association with the appearance of infiltrative behavior but not with degree of
tumor progression (including
metastasis) at the time of resection.