Introduction

Small bowel neoplasms encompass a rare grouping of diseases, ranging from benign and asymptomatic to malignant. The malignant tumors, including adenocarcinoma, neuroendocrine tumors, lymphomas, and sarcomas have appropriately different medical and surgical treatments.

Epidemiology

Small bowel cancer is rare, comprising less than 1% of new cancer diagnoses each year. The estimated incidence of new cases of small bowel malignancies in 2012 is 8,070, with 1,150 deaths. This is in contrast to the estimated new cases of colorectal cancer totaling 143,460, with 51,690 deaths. Small bowel cancer makes up less than 10% of gastrointestinal cancers each year.¹

In 1987, the most common histologic types of malignant tumors of the small intestine in population-based registry data from the Surveillance, Epidemiology and End Results (SEER) program of the National Cancer Institute were adenocarcinoma 45%, carcinoid 29%, lymphoma 16%, and sarcoma 10%.

However, 17 years later, results from 2004 SEER database documented that the overall incidence of small bowel malignancies increased (from 2.1 to 9.3 per million). Carcinoid tumors have now superseded adenocarcinoma in incidence: carcinoid 37.4%, adenocarcinoma 36.9%, lymphomas 17.3%, and stromal tumors 8.4%.² The overall increased incidence appears to be largely due to carcinoid tumors; it is unclear whether this is due to improved imaging, because most carcinoids are asymptomatic.

SEER trends from 1973 to 2000 showed an increasing incidence in black men, who had roughly double the rate of incidence of both carcinoid and carcinoma compared with whites (10.6 vs. 5.6 per million people and 9.2 vs. 5.4 per million people, respectively).³

Location

Distribution throughout the gastrointestinal (GI) tract tends to vary based on type of malignancy. Adenocarcinoma favors the duodenum and jejunum, whereas the ileum contains the majority of carcinoid tumors. Lymphomas and stromal tumors are more evenly distributed.²

Pathogenesis and Risk Factors

The rarity of small bowel cancer has made the study of its pathogenesis difficult. However, the etiology of small intestinal adenocarcinoma may be similar to that of colon cancer because it appears to share the adenoma-carcinoma sequence previously described in colon cancer.⁴ Nevertheless, although the small bowel contains 90% of the mucosa of the GI tract, it is surprising that this results in only 1% to 2% of gastrointestinal malignancies. Previous theories as to why cancer of the small bowel mucosa is so rare compared with the colon include the small bowel’s lower bacterial load and faster transit time of ingested carcinogens. The three main categories of risk factors include environmental, genetic, and chronic inflammatory factors.

Chronic Inflammation

Chronic mucosal inflammation has been noted as a cause for development of adenocarcinoma and lymphoma. A series of patients with inflammatory bowel disease (IBD) at The Mount Sinai Hospital demonstrated that 67% of GI cancers associated with Crohn disease and 96% of those associated with ulcerative colitis were located in diseased bowel.⁹ In this series, seven cancers were found in the bypassed loops of diseased bowel, an operation seldom performed today (Fig. 76-1).¹⁰

Clinical Presentation

In general, small bowel tumors are almost always discovered late because presenting symptoms are vague. Pain, often crampy, is the most common presentation, followed by nausea and vomiting, and then weight loss. Small bowel obstruction tends to occur more often in malignant cases, whereas GI bleeding is more frequent with benign tumors.¹¹ Mean age at presentation is 65 years, with a slight predominance in men.¹² The mean age in Crohn disease–related small bowel cancer is about a decade earlier.^10,13

Adenocarcinoma presents most often in patients between ages 50 and 70 years, but predisposing factors such as Crohn disease may cause an earlier presentation. Prevalence is slightly increased in males. In a series of 491 patients with small bowel adenocarcinoma, the following distribution of presenting symptoms was noted: abdominal pain (43%), nausea and vomiting (16%), anemia (15%), overt GI tract bleeding (7%), jaundice (6%), weight loss (3%), other or no symptoms (9%).¹⁴ More proximal lesions present with nausea and vomiting, and distal lesions present with crampy pain and distention before the onset of vomiting.

Although adenocarcinoma associated with Crohn disease tends to occur in the ileum, isolated cases of adenocarcinoma may occur in the duodenum. Diagnosis is particularly difficult in Crohn disease despite the increased incidence because of the difficulty of surveillance even with the more recent use of capsule endoscopy. The symptoms are difficult to differentiate from the symptoms of obstructing Crohn disease (Figs. 76-2 and 76-3). Physicians should consider this possibility if symptoms recur after a long period of quiescence.

Pathology reports from the population-based Cancer Surveillance Program found that 50% of small bowel adenocarcinoma occurred in the duodenum, and half of those were located in the second portion specifically, despite the fact that the duodenum composes only 4% of small bowel length. Possible explanations are that bile might be carcinogenic, or that the alternating acidic and alkaline environments from gastric and pancreatic secretions may be caustic.¹⁵

Although there is a well-documented increased relative risk of developing intestinal adenocarcinoma in Crohn disease compared with the general population, it is still rare (Fig. 76-4). A 25-year history of regional ileitis only confers a cumulative risk of 2.2%.¹⁶ The authors’ experience at The Mount Sinai Hospital between 1960 and 2009 involved 48 cases of small bowel carcinoma in two series of patients with Crohn disease. The overall average time between initial diagnosis of Crohn disease to diagnosis of small bowel adenocarcinoma was 25.8 years.^10,13

Because early symptoms are vague, these tumors often present at a late stage: 3% present as carcinoma in situ, 12% as stage I, 27% as stage II, 26% as stage III, and 32% as stage IV.¹⁷