Merkel cell (neuroendocrine) carcinoma of the anal canal: report of a case.

Merkel cell tumors are rare neuroendocrine tumors typically found on sun-exposed areas such as extremities. We describe the case of a 42-year-old female with a Merkel cell tumor arising in the anal canal. The tumor was initially thought to represent a hemorrhoid arising during pregnancy and was excised locally after confirmation of extensive metastatic disease. The patient died 13 months after diagnosis with extensive metastatic disease involving the liver. In our search of the world literature there are several reports of neuroendocrine tumors in the rectum; however, no cases of documented Merkel cell tumors arising in the anal canal have been reported. These tumors seem to behave in a very aggressive manner when found in other atypical areas. The presentation symptoms were perianal discomfort and bleeding. Local excision may be the only surgical treatment necessary to control symptoms, given the propensity to early metastases and short life expectancy.