Malignant fibrillo-caveolated cell carcinoma of the human intestinal tract.

The ultrastructural features of a peculiar midgut carcinoid, containing cytoplasmic filaments, fibrils, and caveolae, are presented. Because of the morphologic similarities between the tumor cells and the recently described intestinal caveolated cell, it is proposed that the cells of the reported carcinoid represent the malignant counterpart of this new type of cell. The name suggested for this variant of a tumor of the enterochromaffin group of intestinal endocrine cells is malignant fibrillocaveolated cell carcinoma.