Acanthosis nigricans and a rectal carcinoid.

Malignant acanthosis nigricans is often related to adenocarcinomas of the gastrointestinal tract, but it has also been found to coexist with tumors of the amine precursor uptake and decarboxylation system. It can precede, accompany, or follow the appearance of the underlying tumor. Evaluation of our patient's new-onset acanthosis nigricans led to the discovery of an asymptomatic rectal carcinoid tumor. To our knowledge, this is the first report of acanthosis nigricans associated with a carcinoid tumor of the rectum. It emphasizes the importance of considering underlying malignancy in the evaluation of patients with acanthosis nigricans.