What is KRAS?

Reviewed by Pathologists
December 28, 2025

KRAS is a gene found in nearly all cells in the body. Genes are instructions made of DNA that tell cells how to grow, divide, and function. The KRAS gene provides instructions for making a protein that helps control how cells respond to growth signals.

KRAS is also considered a biomarker. A biomarker is a measurable feature in a tumour, such as a gene change or protein, that provides information about how the cancer behaves or how it may respond to treatment. In pathology reports, KRAS is usually mentioned because testing was performed to identify mutations (changes) that can guide care.

What is the function of KRAS in normal cells?

In normal, healthy cells, the KRAS protein acts like an on–off switch for cell growth.

When a cell receives a signal from outside the cell (such as a growth factor), KRAS briefly turns “on” to help the cell grow or divide. Once the signal is finished, KRAS turns “off.” This tight control helps ensure that cells grow only when needed and stop growing at the right time.

What types of cancer are associated with KRAS?

Changes in the KRAS gene are common in several types of cancer, including:

  • Cancers of the colon and rectum.

  • Lung cancer (especially adenocarcinoma).

  • Pancreatic cancer.

  • Some cancers of the bile ducts and small intestine.

Not all cancers have KRAS mutations, and the presence of a KRAS mutation does not, by itself, determine how advanced a cancer is.

How does KRAS cause cancer?

Cancer develops when cells grow and divide without normal control.

When KRAS is mutated, the protein can become stuck in the “on” position. This causes the cell to receive constant signals to grow, even when it should stop. Over time, this uncontrolled growth can lead to the formation of a tumour.

KRAS mutations are usually acquired, meaning they develop in tumour cells over a person’s lifetime and are not inherited from parents.

Why do pathologists test for KRAS?

Pathologists test for KRAS because it is an important predictive biomarker, meaning it can help predict whether specific treatments are likely to work.

In some cancers, including colorectal and lung cancers, specific targeted therapies are effective only when KRAS is not mutated. If a KRAS mutation is present, those treatments are unlikely to help, and other treatment options may be recommended instead.

Testing for KRAS helps doctors personalize treatment by choosing therapies that are more likely to be effective and avoiding those that are unlikely to provide benefit.

How do pathologists test for KRAS?

KRAS testing is performed on tumour material, usually from a biopsy or surgically removed tissue. In some situations, KRAS can also be tested using a blood sample, often called a liquid biopsy, which looks for tumour DNA circulating in the bloodstream.

Several laboratory methods may be used to test for KRAS, including:

How do KRAS results appear in a pathology report?

KRAS results are usually found in a section of the pathology report called molecular testing, biomarker testing, or ancillary studies. This section summarizes genetic tests performed on the tumour to help guide treatment decisions.

KRAS results are most often reported in one of the following ways:

  • KRAS mutation detected, followed by the specific mutation identified.

  • No KRAS mutation detected, sometimes described as KRAS wild type.

If a mutation is found, the report may list the exact change in the KRAS gene. Your report may also include a short comment explaining how the KRAS result affects treatment options, such as whether certain targeted therapies are likely or unlikely to be effective.

Questions to ask your doctor

  • Was my tumour tested for KRAS?

  • Is KRAS considered a biomarker in my cancer?

  • Were any KRAS mutations found?

  • How do my KRAS results affect my treatment options?

  • Are there other biomarkers or genetic tests that should be performed?

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