[Electron microscopic and biochemical characteristics of the hormonal activity of small-cell lung cancer].

An electron microscopic study of small-cell carcinoma of the human lung showed that tumors identified by light microscopy as small-cell lung cancer were, in actual fact, histologically heterogenous, ranging from those free from any signs of specific cell differentiation, neoplasms with endocrine differentiation, squamous cell cancer, adenocarcinomas to tumors with mixed cell differentiation. Elevated blood-ACTH concentrations occur in patients with tumors which do not incorporate cells with endocrine differentiation. In such cases, activation of ACTH synthesis may be due to hyperfunction and hyperplasia of apudocytes (elements of a diffuse endocrine system--the APUD system) of the lung or other organs in response to tumor growth.