Oncocytic carcinoid of the lung

A case of oncocytic carcinoid of the lung was studied with the electron microscope. This rare tumour is composed of cells acceptable as neuroendocrine cells, oncocytes and cells of an intermediate morphology. Our studies lead us to believe that this tumour develops by oncocytic transformation of neuroendocrine cells in a carcinoid. Two new findings reported in this study are: 1) the occurrence of filamentous inclusions in mitochondria; and 2) calcified spherules which appear to develop in material secreted by tumour cells.