Small bowel tumours are rare, accounting for <5% of all gastrointestinal cancers (despite the small intestine contains over 90% of the mucosal surface area of the GI tract), and in the UK, their incidence is around 2-3 cases per 100,000 per year.
Most small bowel tumours arise from the duodenum (around 55-82% of cases), and less commonly arise from the jejunum (11-25%) or ileum (7-17%).
Small bowel neoplasms can be either benign or malignant:
- Benign tumours – typically adenomas, subclassified as simple villous, tubular, or Brunner’s gland adenomas; less common types are leiomyomas, lipomas, and desmoid tumours
- Malignant tumours – most common types are either adenocarcinomas or neuroendocrine tumours (40% each*); less common types are stromal tumours, sarcomas, and lymphomas
*Adenocarcinomas more commonly affect the duodenum whilst neuroendocrine tumours more commonly affect the ileum
Small intestine adenocarcinomas are believed to arise from pre-existing adenomas through a sequential accumulation of genetic abnormalities (in a model similar to that described for the pathogenesis of colorectal cancer), which can occur over several years.
The tumour suppressor gene p53, which maintains DNA integrity, and the oncogene KRAS, which normally functions in cellular signalling and proliferation, have been implicated in over 50% of small bowel adenocarcinoma cases.
Small bowel tumours are staged using the TNM staging system.
Non-modifiable risk factors for small bowel tumours include increasing age, Afro-Caribbean ethnicity, Crohn’s disease or coeliac disease, and certain genetic conditions (such as MEN-1 syndrome, Lynch syndrome, or neurofibromatosis-1). Modifiable risk factors include smoking, obesity, and alcohol excess.
Most small bowel tumours are initially asymptomatic. However, as they increase in size, they most commonly become symptomatic by causing a small bowel obstruction due to luminal narrowing (or rarely through intussusception). Less common presentations include lower GI bleeding or symptomatic anaemia.
On examination, an abdominal mass may be palpable (25% of cases). In advanced cases (for malignant tumours), cachexia, jaundice, hepatomegaly, or ascites may be present. Neuroendocrine tumours can also present with carcinoid syndrome.
Due to the absence of symptoms or non-specific presentations associated with most small-intestinal neoplasms, such masses are rarely diagnosed pre-operatively.
Blood tests are non-specific for small bowel tumours. Elevated carcinoembryonic antigen (CEA) levels are associated with small-intestinal adenocarcinomas, however only in the presence of liver metastases, whilst elevated serum 5-hydroxyindole acetic acid (5-HIAA) levels is only observed in certain patients with carcinoid syndrome.
In the early stage of the disease, given the non-specific symptoms associated with small bowel tumours, patients may have already undergone normal upper GI endoscopy and colonoscopy.
As such, in the elective setting, for suspected cases of small bowel tumours, MRI enterography is often used to good effect in the diagnosis. Other imaging modalities that can be used include endoscopic ultrasound (EUS) (especially for cancers in the ampullary region) or capsule endoscopy.
However, as the majority of patients present with features of bowel obstruction, often the diagnosis (or suspicion raised) is made via CT imaging, especially if the tumour is large.
Any symptomatic benign small bowel tumour should ideally be resected, either endoscopically or through surgical resection. Choice of intervention depends on patient factors, as well as size and location of the tumour.
Small bowel adenocarcinomas need surgical resection; a wide local resection of the affected bowel is required, along with the corresponding mesentery to achieve regional lymphadenectomy. Adjuvant chemotherapy is likely required for lymph node positive disease (often with a similar protocol as colorectal cancers)
Management of neuroendocrine tumours is discussed here.
At the time of diagnosis, around 70% of patients with a small bowel adenocarcinoma have potentially resectable disease. The 5 year survival for node-positive small bowel adenocarcinoma is between 12-50%.
- Small bowel tumours are rare, accounting for <5% of all gastrointestinal cancers
- Most common benign types are adenomas and the most common malignant types are adenocarcinoma and neuroendocrine tumours
- The most common presentation for small bowel tumours is with clinical features of bowel obstruction
- Where feasible, all small bowel tumours need resection, either endoscopically or surgically