What is the next step for a patient with stage IIIC adenocarcinoma of the sigmoid colon, who underwent robotic-assisted sigmoidectomy and adjuvant chemotherapy with XELOX (oxaliplatin and capecitabine), and now has an increased Northstar Response score despite negative repeat PET/CT, CT CAP, and Guardant Reveal tests?

Management of Increased Northstar Response Score in Stage IIIC Colon Cancer Patient with Otherwise Negative Surveillance Tests

For a patient with stage IIIC adenocarcinoma of the sigmoid colon who has completed adjuvant XELOX chemotherapy and now shows an increased Northstar Response score despite negative imaging and Guardant Reveal tests, the recommended next step is to perform a diagnostic colonoscopy with biopsy of any suspicious lesions, followed by CT scan with contrast of chest, abdomen, and pelvis if not already done within the last 3 months.

Patient Background and Risk Assessment

• The patient has stage IIIC (pT3N2bMx) sigmoid colon adenocarcinoma with high-risk features including 15/20 positive lymph nodes and lymphovascular invasion 1
• Completed adjuvant XELOX (capecitabine and oxaliplatin) chemotherapy from May to September 2023 1
• Recent surveillance tests show:
  • Negative colonoscopy (July 2024)
  • Negative PET/CT and CT CAP (June 2025)
  • Negative Guardant Reveal (June and October 2025)
  • Increased Northstar Response score from 23 to 38 (October 2025) 1

Recommended Surveillance Algorithm

Immediate Next Steps

1. Repeat colonoscopy with biopsy of any suspicious lesions

   • Despite negative colonoscopy in July 2024, the increased Northstar Response score warrants a repeat examination 1
   • Focus on the anastomotic site and entire colon to rule out local recurrence 1

2. CT scan with contrast of chest, abdomen, and pelvis

   • If not already done within the last 3 months (the most recent was in June 2025) 1
   • Pay special attention to the liver, lungs, and peritoneal surfaces as common sites of metastasis 1

3. Serum tumor markers

   • Check CEA levels if not already done 1
   • Elevated CEA may indicate recurrence even with negative imaging 1

If Initial Workup Is Negative

1. Consider PET/CT scan

   • May detect occult metastases not visible on conventional imaging 1
   • Particularly useful if CEA is elevated with negative conventional imaging 1

2. Consider additional liquid biopsy testing

   • The discrepancy between Guardant Reveal and Northstar Response suggests potential early recurrence 1
   • Serial testing may be warranted to confirm trends 1

Rationale for Recommendations

• Stage IIIC colon cancer has a high risk of recurrence, particularly with 15/20 positive lymph nodes 1
• The ESMO guidelines recommend intensive surveillance for patients with high-risk features 1
• An increasing Northstar Response score may indicate early molecular evidence of recurrence before radiographic evidence appears 1
• Early detection of recurrence is critical as it may allow for potentially curative surgical intervention for isolated metastases 1

Surveillance Schedule for High-Risk Patients

• History and physical examination: Every 3-6 months for first 2-3 years, then every 6 months for years 3-5 1
• CEA testing: Every 3-6 months for first 2-3 years, then every 6 months for years 3-5 1
• CT chest/abdomen/pelvis: Every 6-12 months for first 3-5 years for high-risk patients 1
• Colonoscopy: At 1 year after resection, then every 3-5 years if normal 1

Common Pitfalls and Caveats

• False positives: Liquid biopsy tests may occasionally yield false positive results; confirmation with conventional imaging and/or biopsy is essential 1
• False negatives: Conventional imaging may miss small-volume disease; discordance between molecular testing and imaging should prompt further investigation 1
• Timing of surveillance: Most recurrences occur within the first 3 years after primary treatment; this patient is approximately 2.5 years from diagnosis, still in the high-risk period 1
• Interpretation of multiple surveillance modalities: When different surveillance methods show discordant results, the most sensitive test showing abnormality should guide management 1