Small Bowel Tumors

DEFINITION:

Tumors of the small bowel; Fortunately primary neoplasia of the small bowel is rare

EPIDEMIOLOGY:

Small bowel comprises >75% of the length and >90% of the mucosal surface area of the gut, yet the small bowel is the least common site of primary cancer
Prevalence:
- 3-6% of all GI tumors, 75% of these are malignant
- Therefore small bowel cancer accounts for 1-2% of GI malignancies and 0.1-0.3% of all malignancies
Incidence: 10 in 1 million; Low, reasons:
- Small bowel is alkaline, therefore not allowing activation of certain carcinogens; Lots of lymphatic tissue with protective IgA production
- Faster transient time with less exposure to carcinogens, small bowel has higher cell turnover with fewer stem cells (carcinogen target cells)
- Benzpyrene hydroxylase present in high concentrations: converts benzpyrene, a known carcinogen in food, to less toxic metabolite
Risk factors: older age, male, African American, ? Diet
Inheritable conditions with increased risk of small bowel tumors:
- Adenomatous polyposis coli (FAP, Gardner’s): associated with colorectal and duodenal adenomas
- Peutz-Jeghers Syndrome: associated with hamartomas of GI tract; Also increased incident of small bowel adenocarcinoma
- Hereditary nonpolyposis colon cancer (HNPCC) or Lynch II syndrome; Increased incident of small bowel adenocarcinoma
- Von Recklinghausen’s Disease (Neurofibromatosis type 1): associated with occasional schwannomas
- Crohn’s Disease
Immunosuppressed condition with increased risk:
- HIV: will likely be the leading cause of primary GI lymphomas (usually high-grade B-cell non-Hodgkins); Kaposi’s sarcoma too
- Immunosuppression: cyclosporine is associated with increased incidence of small bowel lymphoma in transplant patients
Impaired mucosal barrier with increased risk:
- Crohn’s disease (adenocarcinoma), Celiac disease (T-cell lymphoma), H. Pylori (gastric lymphoma, MALT)

ETIOLOGIES: Terminology; See also Treatment below for further definitions

Tissue of Origin	Benign	Malignant	How Common	Site of Primary Tumor
Mucosa	Adenoma	Adenocarcinoma	20-70% (most common)	Duodenum, jejunum
Enterochromaffin	—	Carcinoid	1-4%	Ileum
Lymphoid	—	Lymphoma (T-cell with Celiac)	3-50%	Ileum, jejunum
Mesenchymal	Benign GIST (Gastrointestinal Stromal Tumor)	Malignant GIST	1% (rare)	Stomach (most common)
Smooth muscle	Leiomyomas	Leiomyosarcomas	Note: GIST previously misclassified in Smooth muscle group
Vascular	Hemangioma	Angiosarcoma
	Lymphangioma	Lymphangiosarcoma
	—	Kaposi sarcoma
Connective tissue	Fibroma	Fibrosarcoma
Nerve	Neurofibroma	Neurofibrosarcoma
	Schwann cell tumor	Malignant schwannoma
Fat	Lipoma	Liposarcoma