Ectopic Cushing's syndrome: clinical, diagnostic, treatment and follow-up outcomes of 12 cases of lung ectopic ACTH

Ectopic Cushing's syndrome (ECS) is a rare disease associated with significant comorbidity. Among the causes of Cushing's syndrome, adrenocorticotropic hormone-producing extrapituitary tumours are rarely reported. This low frequency makes it difficult for the physician to acquire experience in its management.In this report, we aimed to describe the clinical presentation, diagnostic approach and treatment modalities of 12 patients with ECS treated in a single tertiarycentre over a 17-year period. Although they can appear in different locations through the neuroendocrine system, lung tumours are the most frequently reported, as it occurs in our series. They can show different levels of aggressiveness and mild to severe clinical course. Therefore, distinguishing Cushing's disease can be challenging and sometimes requires more specific techniques such as invasive tests or no conventional imaging. Treatment includes controlling both hypercortisolism and neoplastic disease, and multidisciplinary management is recommended. Learning points Ectopic Cushing's syndrome (ECS) accounts for 15% of endogenous Cushing's syndromes. Its infrequency implies that both diagnosis and treatment can be a challenge for clinicians without experience in its management. The most common location is the lung. Although older series reported small cell lung carcinoma (SCLC) as the main ECS-producing tumour, currently most cases are attributed to lung carcinoids. Low-grade tumours (lung carcinoids) present themselves with a more subtle and gradual hypercortisolism, and clinically this can be difficult to differentiate from hypercortisolism due to CD. In contrast, high-grade tumours (SCLC) show severe hypercortisolism with rapid evolution. The diagnostic approach is complex especially when the tumour is not previously known and the clinical presentation is subtle. Functional tests are mandatory in these cases, and nuclear medicine imaging can help when conventional imaging tests fail to identify the tumour. ECS treatment includes a wide variety of modalities oriented to treat both the excess of cortisol and the tumour itself. The tumour prognosis depends fundamentally on the type of adrenocorticotropic hormone-secreting tumour. Expert and multidisciplinary team is essential for successfully treating these complex and ill patients.