The clinicopathological study of serrated adenoma

[Background & Aims] Colorectal polyps have been devided into two histological subtypes: hyperplastic polyps and adenomas. Recently mixed epithelial polyps that combine the morphological features of a hyperplastic polyp with the cytologic features of an adenoma have been reported and termed serrated adenoma. We have detected and designated those polyps as H-type adenomatous polyps since 70s. The aims of this study is to clarify the clinicopathological features and malignant potential of serrated adenomas. [Methods] Between 1974 and 1996, colonoscopic polypectomies for 8858 lesions were performed at our hospital. Of 7800 neoplastic lesions, 148 (1.9%) serrated adenomas have been detected. We devided 23 years (1974-1996) into following three periods according to the number of polypectomy per year: '74 to '83 (-100), '84 to '90 (100-500), '91 to '96 (500-). We examined the rate of serrated adenoma and differences of clinicopathologic factors of each period. [Results] Average age was 58.8 years old and male to female ratio was 2.05. Pathological characteristics were as follows: distribution (rectum 29.7%, sigmoid colon 43.8%, descending colon 6.8%, transverse colon 9.5%, ascending colon 8.8%, cecum 1.4%), the average size (8.9mm), endoscopic configurations (pedunculated 43.2%, semipedunculated 43.2%, sessile 10.2%, flat 3.4%), endoscopic findings (villous-like 25%, adenoma-like 75%), incidence of severe dysplasia (2.7%). All lesions except severe dysplasia showed no staining of p53 immunohistochemically. According to the periods; average age ('74 to '83 56.7, '84 to '90 54.7, '91 to '96 62.2), male to female ratio (1.8, 2.5, 1.9), the rate of serrated adenoma (4.7% [16/341], 2,7% [53/1998], 1.4% [79/5461]), the average size (10.1mm, 7.6mm, 9.4mm). [Conclusions] We have already been able to detect serrated adenomas in the early 70s. Incidence of severe dysplasia and p53 positive rate were relatively low. Therefore the malignant potential of them may not be higher than reported before.