Mucinous carcinoid tumor of the vermiform appendix

Three examples of a distinctive, well-differentiated, mucin-secreting tumor of the vermiform appendix are described. Because of the presence of infiltrating groups of “signet ring” cells, these tumors have often been diagnosed and treated as adenocarcinomas. The demonstration of appreciable numbers of argentaffin cells, particularly in formalin-fixed tissues, as well as the absence of mucosal glandular involvement by tumor tend to support the contention of previous workers that this unique tumor is histogenetically and biologically more akin to a carcinoid tumor. Most of these tumors are not apparent grossly, but are an incidental microscopic finding in an acutely inflamed appendix. In view of the lack of documented aggressive behavior of this lesion, the need for additional surgical treatment beyond appendectomy is questioned.