When patients are diagnosed with colon cancer, the extent of their cancer will be determined by staging, a system which identifies the size of a tumor and whether it has spread beyond the primary site.

How doctors determine staging for colon cancer

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When patients are diagnosed with colon cancer, the extent of their cancer will be determined by staging, a system which identifies the size of a tumor and whether it has spread beyond the primary site.

Staging is helpful to guide treatment and predict outcomes of that treatment. Exact staging isn't usually known until the cancer has been removed and can be evaluated by a pathologist. A physical exam and scans help with staging, but the final stage is determined by the pathology after surgery.

Staging uses the "TNM" system:

  • "T" is for "tumor." This will tell doctors how large the tumor is and how deep it has penetrated through the layers of the colon.
  • "N" is for "nodes," or lymph nodes. This varies depending on whether tumors have spread to nodes and the number of nodes involved.
  • "M" is for "metastasis." This determines if the tumor has spread beyond the colon to tissues around it. If colon cancer spreads, it often will spread to the liver.

The cancer will also be rated as Stage I to Stage IV:

  • Stage I: A Stage I tumor has very little penetration through the colon. It has not spread to the lymph nodes or another area.
  • Stage II: A Stage II  tumor has deeper penetration through the colon but still has not spread to the lymph nodes or another area of the body.
  • Stage III: A Stage III tumor has spread to the lymph nodes but not to any other areas.
  • Stage IV: A Stage IV tumor has distant spread already away from where it started in the colon.

The cancer team will use this information to create the most effective treatment plan for a patient.