Cushing's Syndrome Caused by Corticotropin Secretion by Pulmonary Tumorlets

The term “pulmonary tumorlets” describes multiple microscopic nests of neuroendocrine cells in the lungs.1 Like bronchial carcinoid tumors and small-cell carcinomas, pulmonary tumorlets arise from Kulchitsky's cells. In the lung the abnormalities in these cells range from hyperplasia to malignant transformation, since control over cellular growth is lost.2 Both bronchial carcinoid tumors and small-cell lung carcinomas may secrete corticotropin in sufficient quantities to cause Cushing's syndrome. We describe a patient with Cushing's syndrome due to ectopic secretion of corticotropin in whom the source of the excess corticotropin was ultimately found to be hundreds of tumorlets in one lobe of the . . .