Ultrastructural markers of colonic adenocarcinoma.

A mixed population of 96 adenocarcinomas was examined by electron microscopy to establish the presence of organ specific features. This resulted in the identification of fine structural characteristics, occurring consistently in colorectal adenocarcinomas but not in other epithelial tumors. The colorectal "ultrastructural profile" consists of microvilli with dense cores of microfilaments extending as long rootlets into a clear zone of apical cytoplasm, apical electron dense bodies, and abundant glycocalyceal bodies. Of these features, the long rootlets constitute the best morphologic marker for large intestinal type adenocarcinoma. Using these characteristics in another series of 58 adenocarcinomas studied in a double-blind manner, it was possible to distinguish colorectal adenocarcinomas from other carcinomas on ultrastructural grounds alone.