The Pathology Dictionary Team
June 5, 2023

What is KRAS?

KRAS is a gene that provides instructions for making a protein called K-Ras. The K-Ras protein sends signals from outside of the cell to the nucleus. These signals cause normal, healthy cells to grow and divide.

What is a gene?

Each cell in your body contains a set of instructions that tell the cell how to behave. These instructions are written in a language called DNA and the instructions are stored on 46 chromosomes in each cell. Because the instructions are very long, they are broken up into sections called genes. Each gene tells the cell how to produce a piece of the machine called a protein.

All genes are made of molecules called bases. There are four bases (A, T, G, and C) that make up the genetic code. The order of the four bases determines which proteins are made.

How does KRAS cause cancer?

In normal healthy cells, K-ras protein is only made when the cell needs to grow or divide to create new cells. However, a change in the KRAS gene can cause the cell to produce too much K-ras protein. This kind of change is called a mutation. The large amount of abnormal K-ras protein produced will allow the cell to quickly grow and divide, creating many more cells than the body needs. Over time this group of cells can turn into cancer.

What types of cancer have KRAS mutations?

Mutations in KRAS are commonly seen in cancers of the colon and rectum, pancreas, and lung. Cancers with KRAS mutations may respond better to specific, targeted treatments such as RAS inhibitors.

How do doctors test for KRAS mutations?


Immunohistochemistry is a special type of test that allows pathologists to see the kinds of proteins being made by a cell. Cells with a mutation in the KRAS gene make a K-ras protein that is different from normal cells. Immunohistochemistry can be used to see cells making this abnormal K-ras protein. Positive or reactive means that the tumour cells in your tissue sample are making an abnormal K-ras protein. Negative or non-reactive means that no abnormal K-ras protein was found.

Polymerase chain reaction (PCR)

Polymerase chain reaction (PCR) is a special test that allows pathologists to analyze the bases in one or more genes. By reading the bases in a gene, your pathologist can find cancer-causing mutations.

If a mutation is found in the KRAS gene it will be described in your report as detected or positive. Your report may also say where in the gene the mutation was found. If no mutation is found it will be described in your report as not detected or negative.

Next-generation sequencing (NGS)

Next-generation sequencing (NGS) is a special test used to analyze a large number of genes at the same time. NGS is commonly used to look for mutations in the KRAS gene and other genes that are known to cause cancer.

If a mutation is found it will be described as positive. The location and type of mutation may also be described in your report. A mutation known to cause cancer may be described as pathogenic or likely pathogenic. If no mutation is found, the results will be described as negative.

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