Histopathology of Early Colorectal Cancer

The histopathologic spectrum of early colorectal cancer (ECC) is compared from the Western and Japanese perspective. In the West, most ECC presents as a malignant adenoma, whereas superficial ECC with no adenomatous component is well described in the Japanese literature. Furthermore, superficial ECC is thought to progress rapidly and disseminate early. The discrepant viewpoints are considered in the light of different approaches to histopathologic interpretation. Lesions reported by Japanese pathologists as superficial carcinomas limited to the mucosa are diagnosed as flat adenomas in the West. In one Japanese series only 4 of 218 (1.8%) flat or small sessile neoplasms removed by endoscopic mucosal resection were associated with submucosal invasion by carcinoma. Therefore superficial ECC with submucosal spread is uncommon. Most ECC in hereditary nonpolyposis colorectal cancer evolves through the adenoma—carcinoma pathway (including flat adenoma). However, adenoma removal in the context of population-based screening programs has not lowered the incidence of colorectal cancer; flat colorectal neoplasia may be important in clinical practice.