Oat cell carcinoma of the esophagus with multiple differentiation.

We report an esophageal oat cell carcinoma with multiple differentiation in a 75-year-old man who had a flat lesion with nodular projections in the middle third of the esophagus. Most of the resected tumor consisted of small round cells that contained neurosecretory granules, tonofilaments, and desmosomes. The tumor cells invaded only into the submucosa with extensive intraepithelial spreading. Foci of adenoid cystic, glandular, and squamous differentiation were found in some areas, and had continuity with the intraepithelial spreading carcinoma. Transition was also found. These findings suggest that the small cells had a propensity to undergo further adenoid cystic, glandular, and squamous differentiation.