Updated 3 October 2007
The small bowel represents approximately 75% of the length of the overall GI tract and contains 90% of the gastrointestinal tract surface area but < 5% of GI cancers occur in the small bowel. 1997 epidemiologic data from the United States demonstrated 131,200 large bowel cancers, 22,400 stomach cancers but only 4,900 small bowel cancers. In Canada, 453 small bowel cancers were diagnosed in 2001 (253 male, 200 female) compared to 12,169 large intestine cancers and 2,832 stomach cancers.
Small bowel cancers are rare malignancies with an annual incidence of 0.4 to 1/100,000 in the general population. There are, however, reporting variances amongst tumour registries which make the interpretation of the summary data problematic. For example, lymphomas of the small bowel are rare in industrialized countries and are often not included in small bowel epidemiologic studies. In less developed countries, small bowel lymphoma is the most common type of small bowel malignancy.
Carcinoid tumours, sarcomas and small bowel lymphomas are dealt with in other sections of the management guidelines. The focus of this section will be on adenocarcinomas, the commonest type seen in most Western populations.
Location in Small Bowel
Table 1: Small bowel adenocarcinomas-from population-based series
|
Population |
Anatomic sub site |
|
|
Duodenum |
Jejunum |
Ileum |
NOS |
Total |
|
Los Angeles County |
213 |
108 |
78 |
42 |
441 |
|
Cancer registries of 4 Western provinces |
215 |
115 |
63 |
128 |
521 |
|
Utah Cancer Registry |
29 |
16 |
13 |
22 |
80 |
|
Nine SEER registries |
777 |
376 |
251 |
205 |
1609 |
|
Total |
1234 |
615 |
405 |
397 |
2651 |
|
Percent of total |
46 |
23 |
15 |
15 |
|
Geographic and Ethnic Distributions
There are differences in annual incidence based on geography and ethnicity. For example, New Zealand Maoris have a 5 fold greater annual incidence, 4.2/100,000 population, compared to New Zealand non-Maoris, 0.75/100,000 population. Other populations at higher risk than North American populations include native Hawaiians, Swedes and Brazilians, with lower annual incidences seen in Israelis, Japanese, Latvians, Chinese and Columbians.
Male: Female Ratio
In most registries, males have a consistently higher incidence than females with a range of 1.5-2:1.
Age Distribution
As seen in large bowel cancer, the incidence of small bowel cancer rises with age, with a mean age at diagnosis of 60+/- 10 years.