Small intestine cancer

Small intestine cancer is a location-based description. Adenocarcinoma starts in gland-forming lining cells; neuroendocrine tumors, gastrointestinal stromal tumors and lymphomas arise from other cell types. This guide focuses on adenocarcinoma once that diagnosis is confirmed. A rare sarcoma or neuroendocrine carcinoma requires its own specialist pathway.

The exact site also matters. A duodenal tumor close to the bile duct or pancreas must be distinguished from a cancer starting in the ampulla, bile duct or pancreas. Similar-looking locations do not automatically share the same diagnosis or drug approvals.

Use the pathology name to reach the corresponding guide.

Small bowel tumors can cause intermittent abdominal pain, unexplained anemia, bleeding, weight loss or vomiting. Progressive bloating with vomiting and inability to pass stool or gas may indicate obstruction. Severe pain, collapse or substantial bleeding needs urgent assessment; these problems should not wait for a routine oncology appointment.

CT or MRI assesses the bowel and possible spread. Upper endoscopy can reach the duodenum; enteroscopy can examine deeper segments and obtain tissue. CT or MR enterography may help when ordinary imaging is insufficient. Capsule endoscopy cannot take a biopsy and may become trapped in a narrowed bowel, so suspected obstruction must be evaluated before considering it.

For adenocarcinoma, staging considers invasion through the bowel wall, regional lymph nodes and distant spread. AJCC currently retains its eighth-edition small intestine carcinoma system; small bowel neuroendocrine tumors use separate staging. The pathology report should also describe grade, margins and the nodes examined.

MMR protein testing or MSI analysis is recommended for small bowel adenocarcinoma. An abnormal result can influence treatment and trigger evaluation for Lynch syndrome, but it does not by itself prove an inherited condition. Family history, polyposis syndromes, Crohn’s disease and celiac disease are also relevant to the work-up and longer-term care.

For resectable adenocarcinoma, the aim is complete removal with clear margins and appropriate regional lymph node assessment. Jejunal or ileal disease often allows removal of a bowel segment and reconnection of the ends. Some duodenal cancers require a Whipple operation because of their relationship to the pancreas and bile duct; others may be suitable for a more limited operation after specialist review.

When complete removal is not possible, an operation or endoscopic intervention may still relieve obstruction or bleeding. Such symptom-directed treatment has a different goal from curative resection. Ask what the planned procedure removes, how eating will resume and whether a stoma or additional nutritional support might be needed.

Node-positive disease and selected high-risk node-negative disease warrant an adjuvant discussion. FOLFOX or CAPOX are commonly considered regimens; the expected benefit must be balanced against recovery, kidney function, neuropathy and other health problems. Stage II decisions also take MMR/MSI into account, rather than treating all stage II tumors identically.

The small bowel evidence base is less extensive than that for colon cancer. Retrospective studies suggest benefit in some higher-risk groups, but they cannot establish the effect with the certainty of a randomized comparison. Ask which findings in your pathology justify treatment and which uncertainties remain.

For patients needing chemotherapy, fluoropyrimidine–oxaliplatin combinations such as FOLFOX or CAPOX are commonly used. Choice and intensity depend on prior treatment, symptoms, organ function and fitness. Later treatment may use an irinotecan-based approach or another regimen, but evidence is limited and trial assessment is valuable.

A small bowel adenocarcinoma is not biologically identical to colorectal cancer. A regimen approved for colon cancer is not automatically an established small bowel treatment. Immunotherapy also should not be offered simply because the tumor is rare: the ZEBRA study did not show sufficient activity across an unselected small bowel population, although biomarker-selected responses were seen.

For unresectable or metastatic MSI-high or mismatch-repair-deficient solid tumors, US pembrolizumab labeling includes disease that progressed after prior treatment when no satisfactory alternative exists. This tumor-agnostic indication can include small bowel cancer. It is different from the separate first-line colorectal indication; eligibility and treatment sequence should not be conflated.

Broader profiling may identify rare actionable findings. For example, US trastuzumab deruxtecan has an accelerated indication for previously treated unresectable or metastatic HER2 IHC 3+ solid tumors with no satisfactory alternative. HER2 mutation or amplification alone does not substitute for that protein-expression threshold. Other findings need their own evidence and local approval review.

Nutrition after treatment depends on which bowel segment and how much bowel remain. Persistent diarrhea, dehydration, weight loss or difficulty tolerating meals deserve a dietitian and clinical review. A Whipple operation can create different digestive problems from a short segmental resection. Do not assume that one diet or supplement plan suits both.

During chemotherapy, report significant diarrhea, fever, mouth sores, hand-foot symptoms or increasing numbness early. Follow-up combines symptoms, examination and appropriate imaging or blood tests. Patients with an underlying inherited or inflammatory condition may need additional surveillance beyond cancer recurrence checks.

• Pathology and MMR/MSI results, with the precise segment and primary site.
• Original scans, endoscopy and operation reports, including the bowel removed.
• Treatment dates, toxicities, weight changes, bowel symptoms and any genetic assessment.