Adenocarcinoma arising in the retrorectal space: report of a case

We herein present an extremely rare case of adenocarcinoma of unknown origin arising in the retrorectal space. The imaging and endoscopic findings misled us to preoperatively diagnose a "submucosal tumor." This histological findings were highly suggestive of adenocarcinoma, and its unexpected early and aggressive recurrence required thorough investigation on the true cell type and its origin. Both radiochemotherapy findings and conclusive findings of immunohistochemical staining finally revealed this tumor to be an ordinary adenocarcinoma. It was impossible to identify its origin histologically, because this case was so advanced that it had already replaced the entire entity with adenocarcinoma without leaving any clues as to its former nature. We thus assumed this tumor to be an adenocarcinoma of unknown origin arising in the retrorectal space.