Localised small bowel adenocarcinoma (stage I to III, resected)

Small bowel adenocarcinoma is rare because the small intestine, despite making up most of the length of the gut, produces few cancers. About half arise in the duodenum, where they present with obstruction, bleeding or jaundice and are found at endoscopy, and the rest in the jejunum and ileum, where they are found late after months of obstruction or anaemia; capsule endoscopy, CT enterography and double-balloon enteroscopy have shortened that delay. Predisposing conditions matter: Crohn's disease causes ileal tumours, coeliac disease jejunal ones, familial adenomatous polyposis duodenal and ampullary ones, and Lynch syndrome tumours anywhere, so germline testing and mismatch repair testing are recommended for all patients. Mismatch repair deficiency is found in a larger share than in colon cancer, and HER2 amplification and KRAS mutations in others.

Surgery follows the site: pancreaticoduodenectomy (Whipple procedure) for tumours of the first and second parts of the duodenum, segmental resection with wide lymphadenectomy for the distal duodenum, jejunum and ileum, and right hemicolectomy for terminal ileal tumours, with at least eight nodes examined for accurate staging. Node involvement is the main prognostic factor. No randomised trial had ever tested adjuvant chemotherapy until the international BALLAD trial, which randomised patients with resected stage I to III disease to observation or to fluoropyrimidine chemotherapy with or without oxaliplatin; pending its final results, the NCCN guideline recommends adjuvant CAPOX or FOLFOX for stage III and high-risk stage II disease on the colon cancer model, and considers observation for stage I and low-risk stage II tumours. Mismatch-repair-deficient tumours may gain less from fluoropyrimidines, and neoadjuvant or adjuvant checkpoint inhibition for them is under study. Circulating tumour DNA is being tested to identify patients with residual disease after surgery.