Ectopic Cushing’s From Metastatic Prostate Cancer

Objective: Ectopic ACTH production from malignancy is a rare etiology of Cushing’s syndrome. The most common tumors associated with this syndrome include small cell lung cancer, pancreatic neuroendocrine tumors, pheochromoctoma, thymic carcinoma, and bronchial carcinoma. Metastatic prostate cancer does not commonly produce ACTH. Here, we present a rare case of Cushing’s syndrome due to metastatic prostate cancer. Case Report: Patient is a 64 year old man with a 2 year history of castrate-resistant prostate cancer who was admitted for the 2(nd) time in 1 month for profound weakness and new onset hypokalemia. Initial analysis revealed hypertension with systolic blood pressure in the 150s, potassium in the mid 2s, an ACTH level of >1000pg/mL, and a 24-hr urine cortisol of almost 10,000mcg/24hrs. This was confirmed on repeat analysis. Metyrapone was initiated for treatment of hypercortisolemia and systemic chemotherapy with Cisplatin/Irinotecan was started to treat metastatic prostate cancer. ACTH and 24-hr urine cortisol levels returned to normal within a few weeks of therapy. The patient was able to discontinue Metyrapone following systemic chemotherapy treatment. Subsequent labs following discontinuation of metyrapone confirmed ongoing resolution of hypercortisolemia. Conclusion: This case represents an extremely rare cause of Cushing’s syndrome. Metastatic prostate cancer can rarely produce ACTH and cause clinical Cushing’s syndrome. Ectopic Cushing’s syndrome is often due to very aggressive tumors and is associated with a poor prognosis. Rapid recognition and treatment of this condition can be lifesaving.