KRAS mutation: what it means for your treatment

What does it mean that my tumour has a KRAS mutation?

Reviewed by: Equipo CRC Warriors (pendiente de revisión clínica) Last reviewed: 01/11/2026 Updated: 01/11/2026 2 min
In short: Almost half of colorectal cancers carry a mutation in the KRAS gene. Today the most important consequence is that anti-EGFR antibodies (cetuximab, panitumumab) do not work, so they are not used. Chemotherapy and anti-angiogenic drugs work just as well, and for the G12C variant targeted drugs already exist.

What KRAS is

KRAS is a gene that makes a protein working as a growth switch inside the cell. When it is mutated, the switch is stuck "on" and the cell divides without control. Between 40 % and 45 % of colorectal cancers have a KRAS mutation; the most frequent are G12D, G12V and G13D. The G12C variant is less common in colon cancer (3-4 %) but is the one with the most new drugs.

The mutation is only in the tumour; it is not hereditary and is not passed on to children.

Why it is tested

Guidelines recommend testing RAS (KRAS and NRAS) and BRAF in all patients with metastatic disease, and MSI status in all stages, because it changes treatment:

  • If KRAS (or NRAS) is mutated, anti-EGFR antibodies (cetuximab and panitumumab) are not effective and may even be harmful. That is why they are not part of your treatment.
  • If KRAS and NRAS are normal ("RAS wild-type"), those antibodies are an option, especially in left-sided tumours.

Which treatments do work with mutated KRAS

  • Chemotherapy (FOLFOX, FOLFIRI, CAPOX, FOLFOXIRI) works the same as in tumours without the mutation.
  • Anti-angiogenic drugs (bevacizumab and, in later lines, aflibercept, ramucirumab) are combined with chemotherapy.
  • In later lines: trifluridine/tipiracil (with or without bevacizumab), regorafenib and fruquintinib.
  • If the tumour is also MSI-H/dMMR, immunotherapy is the first option, regardless of KRAS.

Drugs that target KRAS

For decades KRAS was considered "undruggable". That has changed:

  • KRAS G12C: sotorasib and adagrasib block the mutated protein. In colorectal cancer they work much better combined with an anti-EGFR (panitumumab or cetuximab); this is how they were approved in the United States and they are being adopted in Europe. Ask about availability at your hospital or about trials.
  • KRAS G12D and pan-RAS: several drugs are in phase 1-3 trials (for example G12D inhibitors and so-called pan-RAS inhibitors). They are not yet approved, but if your tumour has these variants it is worth checking the trials open in Spain.

What to ask at your appointment

  • Which exact KRAS variant do I have (G12C, G12D, G12V, G13D…)?
  • Have NRAS, BRAF, HER2 and MSI status also been tested?
  • Is there a clinical trial for my variant that I could join?
  • If I progress on the current chemotherapy, what is the planned next step?

Frequently asked questions

Does mutated KRAS mean a worse prognosis?

Overall, KRAS-mutated tumours have a somewhat worse prognosis than RAS wild-type ones, partly because fewer targeted therapies are available, but the difference is moderate and depends a lot on the variant and other factors. BRAF V600E, not KRAS, is the mutation with the greatest prognostic impact.

Can KRAS status change over time?

The tumour's original mutation does not disappear. What does happen is that, after anti-EGFR treatment, some RAS wild-type tumours acquire RAS resistance mutations; that is why the test is sometimes repeated on a liquid biopsy before using those drugs again.

Where does my report say whether I have mutated KRAS?

In the pathology or molecular biology report, in a section usually called "RAS study" or "NGS panel". It appears as "KRAS mutated (p.G12D)" or "KRAS wild-type". If you cannot find it, ask for it: you are entitled to a copy.

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Sources

This guide is general information prepared by the CRC Warriors Association (non-profit) from public medical sources. It does not replace the assessment of your oncologist or medical team, who know your case. If you spot an error, write to contacto@crcwarriors.org.