Clear-cell epithelial neoplasms of the large intestine.

We report four cases of primary clear-cell adenoma and adenocarcinoma of the large intestine. The neoplasms grossly resembled ordinary colonic adenomas and adenocarcinomas but microscopically were composed of uniform cells with optically clear cytoplasm. Mucin stains were negative, and the clear nature of the cytoplasm was due to glycogen accumulation. Areas of transition between normal colonic epithelial constituents and the clear-cell lesion were observed. Three of the four cases stained strongly positively for carcinoembryonic antigen. These lesions are apt to give rise to considerable diagnostic confusion and, in particular, resemble metastatic renal cell carcinoma. The usual strong positive carcinoembryonic antigen reaction is helpful in establishing this diagnosis.