Editorial orientation provided by MedAPI — not part of the coding instruction.
C17 encompasses primary malignant neoplasms arising in the small intestine, including the duodenum, jejunum, ileum, Meckel’s diverticulum, overlapping sites, and unspecified small-intestinal sites. These cancers are uncommon and vary substantially by anatomic site and histology.
Common Histologies
Clinically, small-bowel malignancies include the following; note that ICD-10-CM classifies several of these outside C17:
- Adenocarcinoma — coded to C17.- according to the small-intestinal subsite
- Malignant gastrointestinal stromal tumor (GIST) of the small intestine — classified to C49.A3
- Small-bowel lymphoma — classified within the applicable lymphoma categories, generally C82–C88
- Soft-tissue sarcoma — classified to the applicable C49.- category
Malignant carcinoid tumors of the small intestine are excluded from C17 and classified under C7A.01-. Malignant neoplasm of the ampulla of Vater is classified to C24.1, not C17.0; malignant neoplasm of the ileocecal valve is classified to C18.0, not C17.2.
Common Symptoms
Presentation may be nonspecific or delayed. Findings can include:
- Intermittent abdominal pain (R10.9), nausea (R11.0), or vomiting (R11.10)
- Gastrointestinal bleeding or iron-deficiency anemia (K92.2)
- Unexplained weight loss or fatigue (R63.4)
- Partial or complete bowel obstruction (K56.600)
- Intussusception or, less commonly, perforation (K56.1)
- Jaundice or pancreatitis with tumors of the distal duodenum or in a periampullary location—note that ampullary primaries are coded to C24.1 (C24.1)
- An incidental mass or bowel-wall abnormality on imaging (R93.3)
Diagnosis
Evaluation commonly includes contrast-enhanced CT of the chest, abdomen, and pelvis. CT or MR enterography may better characterize small-bowel lesions. Upper endoscopy can assess the duodenum, while capsule endoscopy or device-assisted enteroscopy may be used for more distal lesions. Capsule retention risk should be considered when obstruction or significant luminal narrowing is suspected.
Histologic confirmation is generally required. Pathology assessment may include tumor type, grade or differentiation, depth of invasion, lymphovascular or perineural invasion, margin status, and regional lymph-node involvement.
Staging
Staging is histology-specific. Small-bowel adenocarcinoma is staged according to primary-tumor invasion, regional nodal disease, and distant metastasis. Common metastatic sites include the liver, peritoneum, distant lymph nodes, and lungs. GIST, lymphoma, sarcoma, and other histologies use different staging or risk-stratification systems.
Stage, TNM elements, and risk stratification are not encoded by C17; they must be documented separately.
Molecular Markers
For advanced small-bowel adenocarcinoma, testing may include mismatch-repair proteins or microsatellite instability, HER2 alterations, RAS/BRAF alterations, and broader genomic profiling for uncommon actionable alterations. Suspected GIST is commonly evaluated for KIT and PDGFRA alterations. Testing should be guided by histology, disease extent, and treatment context.
Common Treatments
- Surgical resection with regional lymph-node assessment for localized adenocarcinoma
- Pancreaticoduodenectomy for selected duodenal tumors when required by location and local extent
- Segmental small-bowel resection for suitable jejunal or ileal tumors
- Systemic chemotherapy for selected node-positive, unresectable, recurrent, or metastatic adenocarcinoma
- Biomarker-directed therapy or immunotherapy for eligible advanced tumors
- Histology-specific treatment for GIST, lymphoma, sarcoma, and other uncommon malignancies
- Endoscopic, surgical, or palliative measures for bleeding, obstruction, pain, or nutritional compromise
Scope Note
C17 identifies the anatomic site of a primary malignant neoplasm of the small intestine, with child codes distinguishing the duodenum, jejunum, ileum, Meckel’s diverticulum, overlapping sites, and an unspecified small-intestinal site. C17.8 applies when a primary tumor overlaps contiguous small-intestinal subsites and its point of origin cannot be determined.
C17 does not by itself encode histology, grade, molecular profile, stage, TNM findings, resectability, or treatment status. Histology-specific classification may place a small-bowel malignancy outside C17, including malignant GIST, lymphoma, soft-tissue sarcoma, and malignant carcinoid tumors classified under C7A.01-. C17 should not be used for secondary or metastatic involvement of the small intestine.