Virus-induced pancreatic cancer in guinea fowl. An electron-microscopical study.

Pancreatic tumors were induced in guinea fowls inoculated with virus strain Pts-56. Sequential high-resolution light microscopic and ultrastructural studies revealed consecutive occurrence of alterations in the pancreas of the infected birds. From the second month p.i., there were nonobligatory, unspecific focal degenerative changes in acinar units that were replaced by tubular complexes, lined with centroacinar-like cells. From the third month, proliferation of ductule structures with mucin-producing or mucin-nonproducing epithelium occurred, giving rise to cystic and papillary adenomas. From the fourth to sixth months, pancreatic adenocarcinomas and poorly differentiated carcinomas arose. The cells of the serous adenomas ultrastructurally resembled the normal pancreatic centroacinar and ductular cells with their regular glandular arrangement on basal lamina, elongated nuclei with finely dispersed heterochromatin, scanty cytoplasmic organelles, microvilli, and occasional cilium. The cells of the mucinous tumors showed similarities to ductal cells with their darker cytoplasmic matrix, larger number of small mitochondria, microfilaments, vesicles, mucin granules, and extensive interdigitations. The cells of the pancreatic carcinomas revealed irregularities in glandular formation, nuclear polymorphism, low cytodifferentiation, and ultrastructural abnormalities, but in most cases retained basic fine structural similarities to the epithelium of the pancreatic ductal system. The present results indicate that the centroacinar cell is the cell of origin of the broad spectrum of pancreatic neoplasms with various differentiation and malignancy induced in guinea fowl by virus strain Pts-56.