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SEER Inquiry System - Report
Produced: 05/05/2026 9:00 PM
Question 20260013
Inquiry Details
References:
#1: Subject matter expert
#2: ICD-O-3, 36. First revision (purple book)
Question:
Primary Site--Colon: How is primary site assigned when the only documented term is “colorectal cancer?” See Discussion.
Discussion:
Patient is diagnosed with adenocarcinoma documented by the physician as “colorectal cancer.” The medical record does not specify colon, rectosigmoid, rectum, or any specific segment of the large intestine. There is also no imaging, operative, endoscopic, or pathology documentation identifying a more precise site of origin.
Specifically, should the registrar assign:
· C18.9 — Colon NOS - (excludes rectum, NOS C20.9 and rectosigmoid junction C19.9)
· C19.9 — Rectosigmoid junction
· C20.9 — Rectum NOS
· C26.0 — Intestinal tract, NOS
· C26.9 — Gastrointestinal tract, NOS
· or another site
Answer:
Assign primary site as colon, NOS (C18.9) when the only information about the diagnosis you have is "colorectal cancer."
We consulted with a subject matter expert who believes that colon, NOS is closest to being correct and that rectosigmoid is not appropriate.
If further information becomes available through further workup and/or treatment, update the primary site as appropriate.
We will add clarification to the 2027 SEER Manual, Appendix C, Colon Coding Guidelines.
