[Rectal cancer (a differential electron microscopic diagnosis)].

A tumor of the rectum in a woman of 74 is described. The analysis of the tumor in light microscope suggested a low-differentiated cancer or melanoma. Electron microscopic examination of the tumor metastasis into a lymph node showed most of the tumor cells to have low differentiation and contain no ultrastructural organspecific markers. However, in the tumor cells comprising a small group, typical tonofibrils and desmosomes were found which substantiated the diagnosis of squamous cell carcinoma.