Fine structure of an oat cell carcinoma of the lung associated with ectopic ACTH syndrome.

Electron-microscopic examination of an oat-cell carcinoma associated with the ectopic ACTH syndrome demonstrated characteristic cytoplasmic granules of 60-240 nm. diameter, consisting of a dense central core separated by a clear halo from an outer investing membrane. Comparison with previously examined non-secretory oat-cell carcinomas showed the granules to be more numerous in the present case. They are considered to represent secretory activity in the tumour.