Essential biomarkers for CRC patients — mutations that block therapy, markers that unlock immunotherapy, and emerging MRD monitoring.
| Biomarker | What It Tells You | Type | Treatment Implications |
|---|---|---|---|
| KRAS / NRAS | RAS pathway mutations (~50% of CRC) | Exclusionary | RAS mutant: anti-EGFR therapy (cetuximab, panitumumab) will NOT work. RAS wild-type: eligible for anti-EGFR |
| BRAF V600E | Aggressive tumor biology (~8–12%) | Targeted | Encorafenib + cetuximab (Braftovi + Erbitux); poor prognosis marker |
| MSI / MMR | Mismatch repair deficiency (~15% stage II–III) | Immuno | MSI-H/dMMR: checkpoint inhibitors (pembrolizumab, nivolumab ± ipilimumab); may not benefit from 5-FU adjuvant |
| HER2 (ERBB2) | Amplification/overexpression (~3–5%) | Targeted | Trastuzumab + pertuzumab, trastuzumab deruxtecan (Enhertu); requires RAS wild-type |
| NTRK Fusion | Rare oncogenic driver (<1%) | Targeted | Larotrectinib (Vitrakvi), entrectinib (Rozlytrek) — tissue-agnostic approval |
| TMB | Tumor mutation burden | Immuno | TMB-High (≥10 mut/Mb): pembrolizumab (tissue-agnostic); less predictive in CRC than MSI |
| ctDNA / MRD | Circulating tumor DNA for minimal residual disease | Monitoring | Post-surgery ctDNA+ predicts recurrence; emerging role in guiding adjuvant therapy decisions |
| CEA | Carcinoembryonic antigen blood marker | Monitoring | Used for surveillance post-treatment; rising CEA may indicate recurrence |
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