What is being tested?
The KRAS an NRAS genes provides instructions for making proteins called K-Ras and N-Ras that are involved in very complex pathways regulating cell division. Both K-Ras and N-Ras bind a molecule called GTP and this switches them on and they become active in the signalling pathway sending signals to the cell nucleus. These signals reaching the nucleus cause the cells to start proliferating and change their behaviour – they differentiate and take on new functions.
Both K-Ras ad N-Ras are GTPase enzymes, they can convert GTP to GDP and when they do so they become inactive. Certain mutations in these genes cause them to lose their GTPase activity and they are then switched on continuously.
How is it used?
In patients with bowel cancer which has spread to adjacent tissues or lymph nodes, the drug cetuximab is usually an effective form of chemotherapy. However, cetuximab is not effective if the bowel cancer has mutations in the KRAS or NRAS genes. This test is used to identify patients in whom chemotherapy with cetuximab is unlikely to be beneficial.
When is it requested?
This test is performed before a doctor recommends a specific therapy for a patient with bowel cancer.
What does the result mean?
Patients with mutations in the KRAS or NRAS gene are unlikely to respond to the chemotherapy, cetuximab, and are prescribed other forms of cancer therapy.
Is there anything else I should know?
In bowel ad some other cancers, the genetic changes in the KRAS and NRAS genes have typically occurred only in the cancer tissue and are not present in other parts of the body.
Common questions
Yes, when mutations in these genes are inherited and thus present in all the cells in the body they can cause several other disorders. However, these are very rare.
Mutations in these genes occur in approximately half of the patients with bowel cancer.
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