What molecular tests and imaging do I need before deciding first-line treatment for metastatic colorectal cancer?

Molecular tests (to guide systemic first-line choice)

• RAS mutation testing (KRAS/NRAS) in all people with metastatic colorectal cancer (mCRC) who are suitable for systemic anticancer treatment. [1]
• BRAF V600E mutation testing in the same cohort (all mCRC suitable for systemic therapy). [1]
• When selecting initial treatment, clinicians commonly consider 3 key molecular markers:
  • BRAF 600 status
  • RAS wild-type vs mutant
  • Microsatellite instability / mismatch repair deficiency (MSI/MMR)
    
    These markers determine eligibility for specific biologic/immunotherapy approaches versus standard chemotherapy backbones. [2]

Imaging (to stage disease before deciding treatment intent and regimen)

• Contrast-enhanced CT chest/abdomen/pelvis to estimate stage in colorectal cancer (and therefore baseline metastatic burden, sites of disease, and potential resectability). [3]
• If metastatic disease is present (particularly liver-limited disease), further imaging may be considered to clarify suitability for resection/local therapy (this affects whether you’re treating with potentially curative intent vs palliative systemic therapy). [4]

Practical decision point

• Use the molecular profile (RAS, BRAF V600E, MSI/MMR) plus full anatomic staging (CT CAP ± further liver-focused imaging if potentially resectable) to decide whether first-line therapy should be:
  • aimed at conversion to resectability (e.g., liver-limited disease), or
  • standard first-line systemic therapy for unresectable metastatic disease. [2]