Appendiceal malignancies.

Malignancies of the appendix are extremely rare. Of the reported cases, carcinoid tumors are most common, with mucinous cystadenocarcinomas and adenocarcinomas next in frequency. Adenocarcinoids, which share morphologic and clinical features that are a composite of adenocarcinomas and carcinoids, have been described. Concomitant second malignancies, most often in the GI tract, occur with greater than expected frequency in patients with appendiceal tumors. Treatment and prognosis are markedly different for each of the histologic variants of appendiceal malignancy. In general, carcinoid tumors (smaller than 2 cm in diameter) may be treated by appendectomy alone and are associated with long term survival. Adenocarcinomas, unless well differentiated and extremely superficial and localized, required hemicolectomy and confer a prognosis that is, stage for stage, similar to that of adenocarcinoma of the colon. Mucinous cystadenocarcinomas may spread widely through the abdomen, resulting in P peritonei, but can be associated with long survival duration if surgical treatment is aggressive. There is evidence that adenocarcinoids develop from simultaneous neoplastic change in two stem cell populations. Metastases may show histologic features of adenocarcinomas alone, of carcinoid tumors alone, or may resemble a composite neoplasm. The prognosis is variable and treatment recommendations are not well defined.