It is difficult to evaluate the infiltration of early protruding colorectal cancer in the anal canal in many cases due to the regional specificity. In particular, rectal lesions may be overestimated employing standard-light observation with retroflex observation.
Furthermore, it is very difficult to assess the degree of infiltration by using endosonography. In this study, we report a patient with early rectal cancer in whom the degree of infiltration was regarded as mucosa, although colonoscopy, including magnified narrow band imaging, digital rectal examination, and endosonography findings, as well as an extremely high serum CEA level, suggested massive infiltration in the submucosal layer.
