Ectopic adrenocorticotropin syndrome associated with undifferentiated carcinoma of the colon showing multidirectional neuroendocrine, exocrine, and squamous differentiation.

We report a rare case of ectopic ACTH syndrome associated with undifferentiated carcinoma of the ascending colon. A 62-year-old woman developed hypokalaemia and metabolic alkalosis associated with markedly elevated serum cortisol and plasma ACTH levels. High-dose dexamethasone (8 mg/day) did not suppress increased urinary 17-hydroxycorticosteroid and 17-keto-steroid excretion. Barium enema and abdominal computerised tomography showed a Borrmann II type tumour in the ascending colon, multiple metastatic nodules in the liver and bilateral enlargement of the adrenal glands. Histological examination of the resected primary colon cancer and metastatic liver tumour showed undifferentiated carcinoma with areas of distinct neuroendocrine, exocrine, and squamous differentiation. ACTH production by the tumour was confirmed by radioimmunoassay and immunohistochemistry. This is a unique case report of carcinoma of the colon with distinct multidirectional differentiation causing ectopic ACTH syndrome.