Endocrine Abstracts

Objective: To report a rare cause of ectopic adrenocorticotropic hormone (ACTH) secretion leading to Cushing syndrome.

Methods: We describe the clinical presentation and management of a case of Cushing syndrome attributable to ectopic ACTH secretion from small cell cancer of the prostate.

Results: In a 74-year-old man developed hypocalemia and heart failure. He was found to have severe hypokalemia (serum potassium, 2.37 mEq/l). Hormonal evaluation revealed a high serum cortisol level of 56.57 microg/dl and a high 24 hour-urine free cortisol excretion of 3218.5 microg/dl (reference range, 4.3 to 176), confirming the diagnosis of Cushing syndrome. A serum ACTH level was elevated at 416 pg/ml (reference range, 0 to 46). An overnight high-dose (8 mg orally) dexamethasone suppression test was positive (serum cortisol levels were 50.3 and 55.1 microg/dl before and after suppression, respectively), and magnetic resonance imaging of the pituitary gland disclosed no abnormalities. Thorax and abdomen CT for ectopic ACTH secreting tumor disclosed no abnormalities too. In PET CT scan, 18 FDG uptake was detected in prostate. Transurethral biopsy of the prostate showed features of small cell prostate cancer. A prostate biopsy specimen showed small cell prostate cancer with highly positive staining for ACTH. The tumor was found to be resectable, but he was in intensive care unit and orotracheal intubated. He was treated with ketoconazole 600 mg/day, which yielded good temporary control of his Cushing syndrome (serum cortisol level was 19.72 microg/dl and serum potasium level was 4.8 mmol/l). After diagnosis, he died 1 month later as a result of influenza pneumonia sepsis.

Conclusion: Ectopic ACTH secretion accounts for 10 to 20% of all causes of endogenous cushings syndrome and is usually associated with neuroendocrine tumors and small cell carcinoma of the lung (up to 50%).

Small cell prostate cancer is a rare subtype that can be associated with ectopic secretion of ACTH and severe Cushing syndrome. With this subtype of prostate cancer, Cushing syndrome should be considered and appropriately managed.