Fine structure of a bronchial oncocytoma

The fine structure of a bronchial oncocytoma is described. The tumour cells are characterized by abundant, normal sized mitochondria with lamellar cristae. Membrane bound protein granules, which measure 0,1 to 0.5 micron in diameter, are also regularly found. Furthermore, all cell organelles involved in protein synthesis occur in oncocytes. The tumour cells lack basement membranes. The protein storing granules of oncocytes are comparable to peptide hormones storing granules. Positive staining with lead hematoxylin and a faint argentaffin staining suggest that oncocytes in the case studied belong to an oncocytic carcinoid. This view is further substantiated by a high serotonin content of the tumour (50.6 microgram/g wet weight).