Non-oat cell small cell carcinoma of the esophagus. Report of a case with ultrastructural observation.

A resected case of undifferentiated, non-oat cell type small cell carcinoma of the esophagus in a 78-year-old Japanese male is presented. Biopsy of a lower esophageal tumor that showed protrusions and centrally ulcerated features on esophageal roentgenograms, was initially misinterpreted as probable malignant lymphoma, because the absence of epithelial arrangement and the presence of abundant fine reticulin fibers encircling individual tumor cells. However, sections of the resected specimen disclosed minute foci consisting of nest formations of tumor cells suggesting an epithelial nature. Electron microscopy demonstrated immature round tumor cells, some of which showed occasional villous projections, desmosomal attachment devices, intracytoplasmic filaments resembling primitive tonofilaments. No neurosecretory granules as have been reported in oat-cell carcinoma of the esophagus were identified in the present case. The results suggest that this tumor is derived from the primitive cells of the esophageal mucosal epithelium or the duct of the esophageal glands. This tumor should be discriminated from oat-cell carcinoma on the basis of its histogenesis.