Ectopic ACTH production from oesophageal neuroendocrine carcinoma causing Cushing syndrome.

Ectopic Cushing syndrome (ECS) occurs when a non-pituitary tumour secretes excess adrenocorticotropic hormone, leading to hypercortisolism. ECS is most commonly associated with small cell lung cancer and pancreatic neuroendocrine tumours, but rarely with oesophageal neuroendocrine carcinoma (NEC). We report the case of a man in the 60s initially treated for locally advanced large cell NEC of the oesophagus who later developed ECS. Oesophageal NECs account for less than 0.04% of all neuroendocrine tumours and carry a poor prognosis, with large cell subtype being particularly uncommon. Despite endocrine-directed therapy, the condition of the patient deteriorated rapidly due to aggressive disease. This case underscores the diagnostic challenges of ECS in rare tumour types and highlights the importance of early recognition and multidisciplinary management to optimise outcomes.