Mixed carcinoid and adenocarcinoma of the appendix: report of 4 cases with immunohistochemical studies and a review of the literature.

Four cases of mixed carcinoid and adenocarcinoma of the appendix were reported. All cases presented with a dominant cecal-appendiceal tumor mass and local metastasis. Two patients had multiple peritoneal implants mimicking primary peritoneal serous adenocarcinoma or carcinomatosis. Histopathologic features of the tumors are similar, with infiltrating microglandular and cribriform patterns of tumor nests, and variable numbers of goblet cells. A literature review of "goblet cell carcinoid" that included nonlocalized cases revealed a significant percentage (>14%) of tumor-associated death, in contrast to the classic carcinoid tumor. Immunohistochemical stains were helpful to separate these tumors from carcinoid tumors and primary peritoneal serous adenocarcinoma. Mixed carcinoid and adenocarcinomas were cytokeratin (CK)-20 positive, and negative or weakly positive for chromogranin A and synaptophysin. Carcinoid tumors were CK20 negative and diffusely positive for chromogranin A and synaptophysin. Peritoneal serous adenocarcinomas were CK20 negative. These cases were clinically aggressive, and 1 patient had multiple recurrences and responded partially to chemotherapy.