Abstract

Almost all colorectal carcinomas have been thought to develop from pre-existing adenomas. However, some colorectal carcinomas can arise directly from normal flat mucosa, and usually form infiltrative mass at the early stage. The carcinogenesis of this infiltrative carcinoma may be different from the well-known adenoma-carcinoma sequence, which usually forms a polypoid mass. The purpose of this study is to investigate the different expression of various oncogenes in polypoid carcinoma and infiltrative carcinoma. We performed immunohistochemical staining on p53, bcl-2, c-erbB-2 and MIB-1 in 29 polypoid carcinomas arised from adenomas, and 21 infiltrative carcinomas. The average tumor size of infiltrative carcinomas (5.5 cm) was larger than that of polypoid carcinomas (3.1 cm), and the polypoid carcinomas were differentiated more than the infiltrative carcinomas. The results of p53, bcl-2, c-erbB-2, and MIB-1 antisera immunoreactivity in the polypoid carcinoma were 79%, 17%, 21%, and 100%, and those in the infiltrative carcinoma were 71%, 29%, 29%, and 100%, respectively. However the diffuse positivities of p53 and MIB-1 antisera were slightly higher in the infiltraive carcinomas (62%, 76%) than in the polypoid carcinomas (55%, 41%) (p=0.63, 0.01). And the results of p53 and c-erbB-2 immunoreactivity in the adenomas were 52% and 17%, respectively, which is significantly lower than that in the polypoid carcinoma(p=0.03, 0.74). The immunoreactivty of bcl-2 in the adenoma was 72%, which was significantly higher than that in the polypoid carcinoma (17%) (p<0.01). In summary, we did not show the significant difference in expression of p53, bcl-2, c-erbB-2, and MIB-1 proteins between polypoid and infiltrative carcinomas. However, the tendency of infiltrative carcinomas having a more aggressive nature suggests another carcinogenetic mechanism is involved in the colorectal carcinogenesis.

• Keywords: Colorectal carcinoma;p53;bcl-2;c-erbB-2;MIB-1;