Colon Cancer Staging: Diagnostic Tests and Procedures After Diagnosis

After a colon cancer diagnosis (usually via biopsy during colonoscopy), a comprehensive staging workup determines the extent of disease (TNM stage) and guides treatment—surgery, chemotherapy, radiation, or targeted therapy.

Standard Staging Workup

1. History & Physical: Digital rectal exam (DRE), lymph node palpation, performance status.
2. Laboratory Studies: CBC (anemia), CMP (liver/renal function), CEA (carcinoembryonic antigen—baseline for monitoring).
3. Contrast-Enhanced CT Chest/Abdomen/Pelvis: Primary for T (depth), N (nodes), M (liver, lung, peritoneum, distant nodes).
4. MRI Pelvis (Rectal Cancer): Gold standard for mesorectal fascia involvement, nodal status, sphincter relationship—guides neoadjuvant therapy.
5. Complete Colonoscopy: If not done fully pre-op; synchrony lesions, polypectomy, tattooing.
6. Biopsy/Pathology Review: Confirm histology, grade, MSI/MMR status (immunohistochemistry/PCR), RAS/BRAF mutation (for metastatic disease).
7. Endorectal Ultrasound (ERUS): For early rectal cancer (T1/T2) local staging.
8. PET-CT: Not routine; reserved for equivocal metastatic lesions or recurrence.
9. Chest X-ray: Sometimes used if CT chest not done; less sensitive.
10. Cardiopulmonary Assessment: Echo, PFTs if major resection planned and comorbidities exist.

Staging Determines Treatment

• Stage I–II: Surgery ± adjuvant chemo (high-risk Stage II).
• Stage III: Surgery + adjuvant chemo (FOLFOX/CAPOX).
• Stage IV: Systemic therapy ± metastasectomy ± local therapy; MSI-H/dMMR → immunotherapy.

Multidisciplinary tumor board review optimizes the plan. Staging is dynamic—restaging occurs after neoadjuvant therapy or at recurrence.