Chapter 28 - Epithelial Neoplasms of the Appendix

Abstract

The classification, nomenclature, and histological criteria of mucinous epithelial tumors in the appendix have been the source of considerable controversy. Mucinous epithelial tumors that penetrate deeply into or through the appendiceal wall and disseminate to the peritoneal cavity, resulting in pseudomyxoma peritonei, were the source of much of this controversy. Their exact nature (benign vs. malignant, invasive vs. noninvasive) was a matter of debate and led to nosological confusion. Historically, they were classified as either ruptured adenomas with dissemination of adenomatous epithelium or as adenocarcinomas. In 2003, the term low-grade appendiceal mucinous neoplasm (LAMN) was introduced for these tumors, and this term is now universally adopted for tumors that show “pushing” or “broad-front” invasion combined with low-grade cytological features. In contrast, tumors with pushing invasion and high-grade cytological features are termed high-grade appendiceal mucinous neoplasms (HAMNs). In modern classification systems, a diagnosis of adenocarcinoma in the appendix requires invasion of an infiltrative, not pushing, nature. Goblet cell tumor nomenclature has also undergone significant recent revision. This enigmatic tumor shows both endocrine and mucinous differentiation and has defied easy nomenclature. Classification of these tumors was particularly complicated when they demonstrated high-grade features. Proposed names for this tumor have included goblet cell carcinoid, crypt cell carcinoma, mixed adenocarcinoma carcinoid, and adenocarcinoma ex goblet cell carcinoid. Recently, these tumors were reclassified as goblet cell adenocarcinoma because they frequently have glandular or mucinous differentiation, they are staged similarly to adenocarcinomas, and chemotherapy regimens similar to those for colorectal adenocarcinoma are used in patients with disseminated tumors.