Metaplastic shadow cells in rectal adenocarcinoma: report of a case with immunohistochemical study.

We report a case of adenocarcinoma of the rectum with foci of metaplastic shadow cells. The patient was a 65 year old man with anemia. Macroscopically the tumor was an ordinary rectal cancer. Microscopically, in addition to the features of moderately differentiated adenocarcinoma invading the subserosa, islands of shadow cells in tumor nests were detected in both primary and one of three pericolic metastatic lymph node lesions. Neoplastic glandular cells showed gradual transition to shadow cells. An antibody specific for high-molecular-weight cytokeratins reacted with the shadow cells and intermediate zone epithelial cells surrounding them, but no CEA, low-molecular-weight cytokeratins or cyclin D1 was detectable in them. Cytokeratin 14 was expressed only in the transitional zone epithelial cells. The intermediate zone epithelial cells were regarded as metaplastic squamous cells, from which the shadow cells were derived. The patient died of multiple liver metastases nine and a half months after surgery. To our knowledge, this is the first report of an immunohistochemical study of rectal adenocarcinoma containing shadow cells not only in the primary lesion but also in a metastatic lymph node.