What is the underlying cause of Cushing's syndrome due to small cell lung carcinoma?

Cushing's syndrome is characterized by excessive levels of cortisol in the body, and in the case of small cell lung carcinoma (also known as small cell lung cancer), the underlying mechanism is ectopic ACTH (adrenocorticotropic hormone) production.

Small cell lung carcinoma is a type of neuroendocrine tumor that can produce hormones inappropriately. In this condition, the cancer cells in the lung secrete ACTH, which stimulates the adrenal glands to produce excess cortisol. This process is not due to a primary defect in the adrenal glands themselves or due to an autoimmune process; rather, it results from the ectopic secretion of ACTH by the tumor.

As a result, the key feature of Cushing's syndrome in this context is not the overproduction of cortisol by the adrenal glands directly but rather the stimulatory effect of excess ACTH from the tumor, leading to adrenal stimulation and cortisol overproduction as a downstream effect. Thus, the correct understanding of this pathology highlights the importance of recognizing ectopic hormone production as a cause of hormonal syndromes associated with malignancies.