Immunohistochemical detection of p21waf1/cip1/sdi1 and p53 proteins in formalin-fixed, paraffin-embedded tissue sections of colorectal carcinoma.

Wild-type p53 protein is a critical participant in G1 cell cycle arrest through the induction of waf1/cip1/sdi1 gene product p21, but mutant p53 proteins have lost transcriptional activity. To know whether the view obtained from studies using cultured cells is adaptable to human solid tumors, the authors immunohistochemically stained p21 and p53 in formalin-fixed, paraffin-embedded tissue sections from 67 cases of colorectal carcinoma. Of these, 54 cancers showed positive staining of p53, whereas p21-positive cells were identified in 46 tumors. However, the proportion of cells positive for these proteins varied considerably among cases, and moreover wide variation in p21 immunoreactivity was noted within the same tumor. Although there was an inverse relationship between p21 and p53 staining in tumors, namely, p21-positive cells were p53 negative and vice versa, an intermingling of tumor cells expressing concomitantly both genes was noted in 34 (51%) of 67 tumors. In these tumors, both proteins were usually moderately stained, but tumor cells intensely coexpressing both were found in one sample. This study supports the notion that although p21 expression is regulated by p53 under physiological conditions, it can be regulated by an additional pathway(s) in solid malignant tumors.