Aims: Serrated adenoma (SA) is a relatively newly defined entity of colorectal neoplasm. In this study, we examined the cell proliferation, DNA ploidy, and clinicopathological features of SA in order to investigate its biological features.
Methods and results: We reviewed 10,532 polypectomy specimens of the colorectum obtained from Japanese cases between 1974 and 1998 at Tohoku University Hospital. In total, 193 cases of SA were detected. We first examined clinical features of these cases by reviewing the charts, and then studied cell proliferation using immunohistochemistry of Ki-67 and topoisomeraseIIa, p53 immunoreactivity and DNA ploidy. Results were subsequently compared with those of tubular adenoma (TA) and hyperplastic polyp (HP). Mean size of SA (8.6 +/- 4.6 mm) was significantly larger than those of TA (7.3 +/- 4.6 mm) and HP (5.6 +/- 3.0 mm). More than 80% of SA were protuberant in macroscopic appearance. SA was located predominantly in the sigmoid colon and rectum. Incidences of concomitant carcinoma in HP, SA and TA were 0.4% (1 out of 263), 4.1% (8 out of 193) and 10.3% (809 out of 7838), respectively. Labeling indices for Ki-67 and topoisomeraseIIa in HP, SA and TA were as follows: Ki-67--24.2%, 30.8%, 39.5% and topoisomeraseIIa--15.3%, 16.1%, 23.9%, respectively. In SA, p53 immunoreactivity was detected in the intramucosal carcinoma co-existing with the serrated component. Two out of the ten SA cases examined demonstrated non-diploid patterns of DNA ploidy.
Conclusion: SA is a distinct colorectal neoplastic lesion with the potential of malignant transformation similar to that of tubular adenoma.