Cushing Syndrome as a Manifestation of Neuroendocrine Prostate Cancer: A Rare Presentation Within a Rare Tumor

Neuroendocrine prostate cancer (NEPC) is a rare entity representing 1% of all prostate malignancies, associated with poor prognosis and often concomitant with paraneoplastic syndromes such as Cushing's syndrome (CS) with ectopic adrenocorticotropic hormone (ACTH) production. We present a case of a 56-year-old man with recent lower urinary tract symptoms hospitalized for pelvic pain, rectal tenesmus, and fatigue. A CT scan documented a large prostatic mass, adenomegalies, and hepatic lesions. Bone scintigraphy showed dispersed osteoblastic metastization. The patient had uncontrolled hypertension and hypokalemia that lead to the diagnosis of paraneoplastic ACTH-dependent CS. Prostate biopsy confirmed small cell NEPC. Potassium supplementation, anti-hypertensive medication, and metyrapone were initiated. The patient was proposed for palliative chemotherapy but died within a few days from a urinary tract infection. The authors aim to draw attention to a case of paraneoplastic CS, a rare manifestation, within the rarity that is NEPC.