Small cell carcinoma of the pancreas in association with a choledochal cyst: immunohistochemical characterization and complete response to combination chemotherapy.

Carcinomas arising in choledochal cysts are well recognized; however, small cell carcinomas have not been reported to arise in choledochal cysts. Extrapulmonary small cell carcinomas have been recognized as unique clinicopathologic entities for decades, and have been found arising in numerous sites. Recently there have been several reviews of the subject (Remick et al.: Medicine 66:457-71, 1987; Richardson and Weiland: Seminars in Oncology 9:484-496, 1982; Levenson et al.: Journal of the National Cancer Institute 67:607-612, 1981). Small cell carcinoma of the pancreas has only rarely been described (Reyes and Wang: Cancer 47:2500-2502, 1981; Corrin et al.: Cancer 31:1523-1527, 1973). These tumors must be distinguished from carcinoid tumors and islet cell tumors, which can often lead to histochemical and histologic confusion (Richardson and Weiland: Seminars in Oncology 9:484-496, 1982). Their response to therapy has not been well documented. We report here a small cell carcinoma of the pancreas that arose within a choledochal cyst and that had immunohistochemical characteristics supporting a neuroendocrine origin but that lacked evidence of islet cell differentiation. A complete response to chemotherapy is also described.