Incidence and Malignant Potential of Non-polypoid and Polypoid Colorectal Neoplasms at National Cancer Center, Tokyo

Abstract

Background: Non-polypoid colorectal neoplasms are suspected of having a higher incidence of invasive carcinoma compared to polypoid lesions of similar size. However, non-polypoid lesions have been scarcely studied. The aim of this study was to clarify the incidence and malignant potential of non-polypoid and polypoid lesions. Materials and Methods: A total of 6437 colorectal adenomas and early carcinomas resected between 1998 and 2002 were retrospectively analyzed. Lesions were classified based on their endoscopic appearance: Non-polypoid (IIc, IIa+IIc, Is+IIc) or Polypoid (Ip, Isp, Is, Is+IIa, IIa). Results: There were 153 (2.4%) non-polypoid and 6284 (97.6%) polypoid lesions. There were 69 (45.1%) adenomas, 12 (7.8%) intramucosal carcinomas (m-ca) and 72 (47.1%) submucosal carcinomas (sm-ca) in the non-polypoid group and 5397 (85.9%) adenomas, 778 (12.4%) m-ca and 109 (1.7%) sm-ca in the polypoid group. Among all adenomas, 69 (1.3%) were non-polypoid and 5397 (98.7%) polypoid neoplasms. Counting all the m-ca, 12 (1.5%) were non-polypoid and 778 (98.5%) polypoid lesions. Among all sm-ca there were 72 (39.8%) non-polypoid and 109 (60.2%) polypoid neoplasms. The rate of submucosal invasion was 85.7% (72/84) and 12.3% (109/887) in the non-polypoid and the polypoid early carcinomas respectively (p<0.0001). There were 20 (27.8%) lesions less than 10mm in non-polypoid sm-ca. Meanwhile there were 18 (16.5%) lesions less than 10mm in polypoid sm-ca (p=0.07). The rate of lymph node metastasis was 13.8% (9/65) and 9.5% (7/74) in non-polypoid and polypoid lesions respectively (p=0.42). Conclusion: In spite of its low frequency, non-polypoid lesions account for almost 40% of submucosal colorectal carcinoma. In cases of non-polypoid lesions associated to early carcinoma the risk of submucosal invasion is remarkably high. Special attention must be paid to these lesions in screening colonoscopy.