Also Known As
Formal Name
Kirsten RAS oncogene; V-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog; NRAS (neuroblastoma RAS viral (v-ras)
This article was last reviewed on
This article waslast modified on 23 October 2017.
At a Glance
Why Get Tested?

To determine whether a cancer, usually a large bowel (colorectal) cancer is positive for KRAS or NRAS gene mutation, which helps to guide treatment and determine outcome. RAS gene mutation analysis is also used in the assessment of some other cancer types including head and neck cancer.

When To Get Tested?

If you have been diagnosed with a cancer and your doctor wants to determine whether the KRAS and NRAS genes are mutated in the tumour. If the KRAS or NRAS genes are mutated, the cancer will not be responsive to treatment with RAS targetted therapy.

Sample Required?

A sample of cancer tissue obtained during a biopsy. Generally this test is done on the biopsy taken for initial diagnosis and a second biopsy is not necessary.

Test Preparation Needed?


On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

The biopsy or resection specimen tissue are stored by the pathology laboratory for at least ten years. This means that the test can be undertaken on this “archive” material at any stage in the future if disease becomes evident at a different place in the body (metastatic disease).

Testing for RAS gene mutations has recently become very important in determining the best form of treatment for metastatic colon cancer. RAS is involved in passing signals within tumour cells which result in growth of the tumour (via the RAS-RAF-MAP kinase pathway). The gene which is responsible for RAS signalling occurs in two different forms; mutated (abnormal) and wild-type (normal). 

Approximately 40% of patients with metastatic colon cancer have a tumour with a mutated RAS gene. These patients are unlikely to respond to treatment with anti-epidermal growth factor receptor therapies such as cetuximab and panitumumab. Treatment using these drugs is not recommended for patients with mutated RAS gene as they would suffer from unwanted side effects of the drug without getting any benefit. 

Patients with metastatic disease who have normal (wild-type) RAS genes are likely to respond to either cetuximab or panitumumab. 

In the UK, RAS gene testing is recommended in all patients with metastatic colorectal cancer. There is a good correlation between RAS gene mutation status in the primary tumour and metastases. Stored biopsies or resection specimens of the primary tumour taken months or years before the onset of metastatic disease can be tested for RAS gene mutation at a later date.

How is the sample collected for testing?

A sample of cancer tissue is obtained by doing a fine needle aspiration, needle biopsy, or surgical biopsy/excision

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

Accordion Title
Common Questions
  • How is it used?

    Patients with metastatic colon cancer and wild-type (normal) RAS gene status may be offered treatment with drugs such as cetuximab (Erbitux) and panitumumab (Vectibix). These drugs are known as epidermal growth factor receptor inhibitors. Those patients who have the mutant type of RAS gene will not derive benefit from treatment with these agents.

  • When is it requested?

    RAS mutation testing is recommended as part of the workup of patients with metastatic colorectal cancer. It helps the doctor determine treatment options and understand more about the cancer’s characteristics.

  • What does the test result mean?

    Patients whose tumours have a mutated RAS gene are unlikely to respond to treatment with anti-epidermal growth factor receptor therapy such as cetuximab and panitumumab. Patients with metastatic disease with wild-type (normal) RAS genes are likely to respond to these treatments, which improve the overall response to chemotherapy.

  • Besides RAS what other laboratory tests may my doctor request on my colorectal cancer tissue?

    "All-RAS" testing (testing for both KRAS and NRAS) is currently the only additional test that oncologists will routinely request if metastatic disease is found.

  • If the tumour is RAS mutated, does this mean that the tumour will not respond to any chemotherapy?

    No, tumours often respond to conventional chemotherapy. However, the improved response which is seen in some patients with the addition of epidermal growth factor receptor inhibitors will not be seen in patients with mutated RAS genes. This additional treatment is not indicated in patients with mutated RAS genes.