DEPRESSED ADENOMA OF THE COLORECTUM - ANALYSIS OF PROLIFERATIVE ACTIVITY USING IMMUNOHISTOCHEMICAL STAINING FOR PROLIFERATING CELL NUCLEAR ANTIGEN (PCNA)

Recently, depressed adenomas (DA) of the colorectum have been frequently detected in Japan. The natural history and carcinogenesis of these DA remain unclear. The histological features and cell kinetics of 13 DA were analyzed, using proliferating cell nuclear antigen (PCNA), and compared with 24 non-depressed adenomas (NDA), 12 non-neoplastic mucosa and 12 adenocarcinomas. The DA had a characteristic architecture when compared with the NDA, as demonstrated by a crowded collection of adenomatous tubules with small diameters. The adenomatous tubules tended to occupy the full thickness of the lamina propria at the center with superficial growth to the periphery. The PCNA-positive cells were mostly restricted to the lower half of the crypts in the non-neoplastic mucosa, and were distributed predominantly across the upper half area of the crypts in both the DA and NDA, whereas they were randomly distributed across any area in the adenocarcinomas. The mean labeling index of PCNA in the DA (43.2%) was significantly higher than that in the non-neoplastic mucosa (26.5%) and NDA (29.3%), but lower than that in the intramucosal component of the adenocarcinomas (70.0%). The DA should be seriously considered as a precancerous lesion because of its unusual histologic architecture and high proliferative activity.