| Entity | Definition/notes | Approx share or incidence (if in evidence) | Typical location | Key citations |
|---|---|---|---|---|
| SBC umbrella | Small bowel cancer is a rare malignancy of the small intestine comprising four main histologic groups: adenocarcinomas, neuroendocrine tumors, stromal tumors, and lymphomas. Reviews note adenocarcinoma and neuroendocrine tumor are the two most common categories. | Accounts for ~2.3% of digestive cancers; adenocarcinoma and neuroendocrine tumors each represent ~40% of SBC; duodenum is most commonly involved (55–82%), followed by jejunum (11–25%) and ileum (7–17%). | Duodenum most common overall; then jejunum and ileum. | (pqac-00000000) |
| SBA | Small bowel adenocarcinoma is the epithelial adenocarcinoma subtype of SBC; prognosis is often limited by late diagnosis and management complexity. In hereditary settings, it can arise through an adenoma-carcinoma sequence, especially in Lynch syndrome. | Included within the ~40% adenocarcinoma share of SBC; SEER-based prognostic study analyzed 2,064 SBA cases diagnosed 2010–2020. | Often duodenal overall; in Lynch syndrome, nearly 50% of small bowel cancers occur in the duodenum. | (pqac-00000000, pqac-00000028) |
| SiNET | Small intestinal neuroendocrine tumor (midgut/small-bowel NET) is a well-differentiated neuroendocrine neoplasm of the small intestine; commonly SSTR-positive and often slow-growing but prone to mesenteric nodal/liver spread. | Small intestine NET incidence ~1.2–1.41 per 100,000 persons in recent US SEER analyses; small bowel NETs are among the most common GEP-NET sites; 10-year overall survival reported at 51.7% in one SEER-based analysis. | Frequently ileal/midgut; ileal/ileocecal primaries are emphasized in treatment reviews. | (pqac-00000002, pqac-00000003, pqac-00000005, pqac-00000023) |
| Small intestine GIST | Gastrointestinal stromal tumor is the principal mesenchymal/stromal tumor category of the small intestine, usually driven by KIT or PDGFRA alterations and characterized by KIT (CD117) expression in >95% of cases. | Small intestine is the primary site in ~31% of GISTs; global GIST incidence ~10–15 per million people; small intestine GIST incidence increased by 2.7% annually in SEER 2000–2019. | Small intestine is a major primary site after stomach; may present as multifocal disease in NF1-associated cases. | (pqac-00000001, pqac-00000004, pqac-00000016, pqac-00000017) |


*Table: This table summarizes the disease scope of small intestine cancer, highlighting the umbrella category and the major clinically important histologic subtypes. It is useful for orienting a knowledge base entry to the main entities, their approximate frequencies or incidence, and their usual anatomic distribution.*