Small bowel cancer is a rare malignancy representing approximately 2% of gastrointestinal neoplasms (1). In 2009, it was estimated that 6230 new cases of small bowel cancer and 1110 small bowel cancer–related deaths would occur (1). Most cancers of the small intestine are adenocarcinomas. Because of the nonspecific clinical presentation of small bowel adenocarcinoma and the difficulty in imaging the small bowel, most patients with small bowel adenocarcinoma present with lymph node involvement or distant metastases. Even in patients with localized disease who undergo resection with curative intent, the prognosis is poor, and no studies have yet demonstrated a clear benefit from adjuvant therapy. However, there have been some recent advances in the use of chemotherapy as palliative treatment. In this chapter, the epidemiology, diagnosis, and treatment of small bowel cancers, in particular small bowel adenocarcinoma, are reviewed.
Based on an analysis of the Surveillance, Epidemiology, and End Results database, the age-adjusted incidence rate for small bowel cancers has slowly increased from 0.9 per 100,000 persons in 1973-1982 to 1.8 per 100,000 persons in 2000-2004 (2,3). The majority of this increase has been attributed to an almost three-fold increase in the incidence of carcinoid tumors (4). Among the 14,253 cases of small bowel cancer diagnosed between 1985 and 1995 in the American College of Surgeons' National Cancer Database, 35% were adenocarcinomas, 28% were carcinoid tumors, 21% were lymphomas, 10% were sarcomas, and 6% were other histologic types (5). The incidence of histologic subtypes varies in the different sections of the small intestine, with adenocarcinomas representing 80% of duodenal cancers and carcinoids representing 60% of ileal cancers (6).
The incidence of small bowel adenocarcinoma peaks in the seventh and eighth decades of life, with a mean age at diagnosis of 65 years. A slightly increased incidence is seen in men and blacks (7).
One of the more interesting aspects of small bowel adenocarcinoma is its rarity in comparison to large intestine adenocarcinoma. Even though the small intestine represents approximately 70 to 80% of the length and over 90% of the surface area of the alimentary tract, the incidence of small bowel adenocarcinoma is 30-fold less than the incidence of colon adenocarcinoma. Numerous theories have been proposed to explain the small intestine's relative protection from the development of carcinoma. Proposed protective factors have centered around two concepts. First, the rapid turnover time of small intestinal cells results in epithelial cell shedding prior to the necessary acquisition of multiple genetic defects. Second, the small bowel's exposure to the carcinogenic components of our diet are limited due to a rapid small bowel transit time, the lack of bacterial degradation activity that occurs in the small bowel, and the relatively dilute, alkaline environment of the small bowel.
The small intestine is divided into three sections. The duodenum represents the first 25 cm of the ...