Immunohistological study on the ACTH producing islet cell carcinoma of the pancreas

ACTH producing cells in islet cell carcinoma associated with Cushing's syndrome were studied by an improved immunoperoxidase as well as immunofluorescence technique. The cells which contained ACTH antigen were distributed throughout the tumor tissue of both primary and metastatic lesions in rather small numbers. In the small cancer nests they were present in an irregular or mosaic pattern and, on the contrary, they tend to line along the margin in the larger nests. The intracytoplasmic localization of the ACTH antigen was characteristically demonstrated in the infranuclear area of the tumor cells, closely simulating that of the argentaffin granules of the enterochromaffin cells. The electron microscopic observation identified membrane enclosed, cored granules, 200-300 nm in diameter, present in clusters in the infranuclear area of some tumor cells, which were considered corresponding well to the ACTH positive cells in immune staining.