Ectopic ACTH syndrome associated with anorectal carcinoma. Report of a case and review of the literature.

A 25-year-old black homosexual was noted to be hypertensive, hypokalemic, and to have a rectal mass. Histopathology of the biopsied lesion revealed a mixture of poorly differentiated squamous cell and undifferentiated small cell carcinoma. Abdominopelvic CT showed multiple liver metastases, minimal local tumor extension, and normal adrenal glands. Despite aggressive treatment, he remained hypertensive and hypokalemic. Endocrine work-up revealed: normal 24-hr VMA and catecholamines, normal serum aldosterone and renin levels, elevated urinary free cortisol (3360 micrograms/24 hr), elevated serum cortisol (60 micrograms/dl), and elevated serum ACTH (1697 pg/dl). Liver biopsy confirmed metastatic anorectal carcinoma, and immunohistochemical stains of the rectal biopsy were positive for ACTH and neuron-specific enolase. Although many types of neoplasms have been associated with ectopic ACTH production, small cell carcinoma of the lung is the most common. While there are many reports of colorectal and anorectal neuroendocrine small cell carcinomas, few of these tumors have been associated with clinical ectopic hormone production. This case represents the first report of the ectopic ACTH syndrome associated with anorectal carcinoma.