Tumor Tip of the Week-01-30-2026 GI Unknown Primary

01-30-2026

Scenario: Diagnosed

CT A/P- Impression: No acute intrathoracic process. Extensive metastatic disease of the liver.

Liver bx: Involved by poorly differentiated carcinoma. Comment: The tumor morphology and immunoprofile are non-specific. The differential diagnosis includes metastatic carcinoma from the upper GI and pancreatobiliary origin.

Hem Onc note: Image-guided bx confirmed metastatic poorly differentiated carcinoma. The differential diagnosis includes metastatic carcinoma from the upper GI tract and pancreatobiliary origin.

Question: How would you assign the Primary Site?

• C22.0 Liver; hepatic, NOS
• C22.1 Intrahepatic bile duct
• C25.9 Pancreas, NOS
• C26.0 Intestinal tract, NOS
• C26.9 Gastrointestinal tract, NOS
• C80.9 Unknown Primary Nos

Answer: C26.9 Gastrointestinal tract, NOS

ICD0-3 Coding guidelines for topography and morphology

SINQ https://seer.cancer.gov/seer-inquiry/inquiry-detail/20061034/ Code the primary site according to the physician’s opinion. An ill-defined site code or an NOS code for the organ system is preferred over C809 [Unknown primary site] whenever possible. Code C809 only when there is not enough information to use an ill-defined or NOS code.

SINQ https://seer.cancer.gov/seer-inquiry/inquiry-detail/20140008/

Primary site: If text supports a pancreatobiliary primary with no other information, assign C269 in the absence of any additional information.