Written and medically reviewed by: Assoc. Prof. Cengiz Dibekoğlu, MD, General SurgeryLast updated:
Molecular Testing in Colorectal Cancer
MMR/MSI for new CRC when guidelines support it; RAS/BRAF and selected HER2/NTRK contexts guide advanced therapy and Lynch evaluation.
New colorectal cancers are usually assessed for MMR/MSI status in line with current guidelines — informing immunotherapy discussions and Lynch syndrome work-ups at any age when indicated. In metastatic disease, extended RAS and BRAF testing directs anti-EGFR strategies; HER2 and rare NTRK fusions matter in defined subsets. Using these results prevents ineffective antibodies and opens targeted options. Order tests that answer a stage-specific question rather than collecting unused data.
Educational schematic. Some structures may be simplified or emphasized for clarity; not an exact anatomical depiction.
© Cengiz Dibekoğlu — illustrative; not for unauthorized use
Figure summary
This educational figure shows: Colorectal.
Who may be a candidate?
- International patients preparing a structured second-opinion visit
- Patients comparing observation, medical care, and procedural options
Possible advantages
- Supports informed consent with alternatives and recovery themes
- Highlights red flags that should trigger urgent contact
Limits & realistic expectations
- Cannot replace examination, imaging, or pathology
- Local protocols and tumor-board decisions may refine timing
- Outcomes vary with anatomy, stage, and comorbidity
Step-by-step overview
- 1
Clarify the clinical question
What diagnosis is being confirmed and what decision follows?
- 2
Choose first-line tests
Start with the test that answers the leading question safely.
- 3
Stage if needed
Add imaging or endoscopy when results would change management.
- 4
Name limitations
No test replaces exam; false reassurance is a risk.
- 5
Link to next step
Diagnosis should point to observation, medical care, or procedure.
Key points
- Key note inside
Somatic vs germline
Tumor-only findings are not automatically hereditary. Germline counseling uses separate consent and cascade-testing rules. Discuss timing, alternatives, and follow-up with your surgical team before you finalize a plan.
- Key note inside
Important
This page is for education. It is not medical advice and does not replace a visit with your physician.
Frequently asked questions
Why is MMR/MSI tested in new colorectal cancer?
It informs immunotherapy discussions and Lynch syndrome evaluation — not only in young patients.
When are RAS and BRAF needed?
Especially before many anti-EGFR strategies in metastatic disease.
Does a normal family history rule out Lynch syndrome?
No. Abnormal MMR can still trigger germline evaluation.
What if tissue is insufficient?
Repeat biopsy or, in selected cases, circulating tumor DNA may be discussed.
More chapters in this hub
Molecular Testing Overview
Biomarkers answer specific treatment and hereditary questions
Molecular Testing in Gastric Cancer
HER2, PD-L1, CLDN18.2, and MSI/MMR timing
Molecular Testing in Breast Cancer
ER/PR/HER2 foundations and germline BRCA framework
Molecular Testing in Pancreatic Cancer
Germline testing is discussed for most patients; tumor profiling in advanced disease
Hereditary Cancers
Lynch, BRCA, FAP, CDH1, and genetic counseling in surgical patient language
Appointment / info
This page is for education. It is not medical advice and does not replace a visit with your physician.
Medical editor: Assoc. Prof. Cengiz Dibekoğlu, MD · Last medically reviewed: August 2026 · English patient-education chapter.