The KRAS gene is in the Ras family of oncogenes, which also includes two other genes: HRAS and NRAS. This gene provides instructions for making a protein called K-Ras that is involved primarily in regulating cell division.
As part of a signaling pathway known as the RAS/MAPK pathway, the protein relays signals from outside the cell to the cell’s nucleus. These signals instruct the cell to grow and divide or to mature and take on specialized functions (differentiate). It is interesting that although most mutations in genes are expected to cause their inactivation, with the Ras genes the opposite happens – they become more active in signaling.
The KRAS Mutation and Cancer
The K-Ras protein is a GTPase, which means it converts a molecule called GTP into another molecule called GDP. The K-Ras protein acts like a switch, and it is turned on and off by the GTP and GDP molecules. To transmit signals, the K-Ras protein must be turned on by attaching (binding) to a molecule of GTP. The K-Ras protein is turned off (inactivated) when it converts the GTP to GDP. When the protein is bound to GDP, it does not relay signals to the cell’s nucleus.
Somatic mutations in the KRAS gene are involved in the development of several types of cancer, including pancreatic, colorectal and non-small cell lung cancer.
Mutations of the K-Ras gene occur in over 90%The Genetics of Pancreatic Cancer http://pathology.jhu.edu/pancreas/geneticsweb/K-ras.htm of pancreatic carcinomas and this is the predominant driver mutation for the development of pancreatic cancer. No other human tumor comes close in mutational frequency. Pancreatic cancer is now the third leading cause of cancer-related death in the U.S. with a 5-year survival rate of only 8%. In 2016, more than fifty-three thousand people in the U.S. will be diagnosed with pancreatic cancer and nearly forty-two thousand will die from the disease. Importantly, 71% of patients die within the first year of diagnosis.Pancreatic Cancer Action Network https://www.pancan.org/wp-content/uploads/2016/11/2016-GAA-PC-Facts.pdf
Mutations in KRAS occur in approximately 30%-50%Medscape Colorectal Cancer and KRAS/BRAF – April 26, 2016 http://emedicine.medscape.com/article/1690010-overview?pa=5Jq32LpUYMFWxC3xr%2B2t15RSYyIhPHSMO7%2Fq%2FNVF1pyQ5JEX7vs%2FxkNm5edN01H6YogTQJgmlryOawBeQxt8WeN5lPYw%2FtQ7Z8WOOzpssmw%3D of colorectal cancers (CRC). A KRAS mutation is predictive of very poor response to the targeted therapies panitumumab (Vectibix®) and cetuximab (Erbitux®) in patients with colorectal cancer. Currently, the most reliable way to predict whether a colorectal cancer patient will respond to one of these drugs is to test for certain “activating” mutations in the gene that encodes KRAS. Studies have shown that patients whose tumors express the mutated version of the KRAS gene will not respond to cetuximab or panitumumab. Although presence of the wild-type (or normal) KRAS gene does not guarantee that these drugs will work, a number of large studies have shown that cetuximab has significant efficacy in metastatic CRC patients with KRAS wild-type tumors. In addition to predicting poor response to targeted agents, emergence of KRAS mutations is a frequent driver of acquired resistance to targeted therapies in colorectal cancers.
Non-Small Cell Lung Cancer
In non-small cell lung cancer (NSCLC), KRAS is mutated in approximately 25%My Cancer Genome – KRAS in NSCLC https://www.mycancergenome.org/content/disease/lung-cancer/kras/ of patients. Knowledge of a patient’s KRAS mutation status helps to predict how patients will respond to the certain targeted therapies. Patients who are positive for the KRAS mutation tend to have a much lower response rate to targeted therapies.
Mutations in the KRAS gene are one of the most frequent genetic abnormalities in ovarian carcinoma. In ovarian cancer, mutations most often affect codons 12 and 13 of the KRAS gene, with mutation rates reported to be as high as 3–11%Mayr D, Hirschmann A, Lohrs U, Diebold J: KRAS and BRAF mutations in ovarian tumors: a comprehensive study of invasive carcinomas, borderline tumors and extraovarian implants. GynecolOncol. 2006, 103 (3): 883-887. 10.1016/j.ygyno.2006.05.029.Caduff RF, Svoboda-Newman SM, Ferguson AW, Johnston CM, Frank TS: Comparison of mutations of Ki-RAS and p53 immunoreactivity in borderline and malignant epithelial ovarian tumors. Am J SurgPathol. 1999, 23 (3): 323-328. 10.1097/00000478-199903000-00012..
Traditional Testing for KRAS
Testing for the presence of a KRAS mutation has traditionally been performed on a tissue biopsy specimen obtained from the patient.
Up to 25%JCO 2015 33 (25) Future Oncol 2015 11(3) of tissue biopsies do not have enough cancer cells to analyze, leading to inconclusive results. Tissue biopsies can be painful, carry risks such as bleeding or infection, and increase the emotional and physical burden of cancer care. Additionally, tissue biopsy results may take up to 30 days to receive, potentially delaying the information needed to select the appropriate treatment. Scans and tissue biopsies add significant cost over the course of treatment and may add to cancer-related stress and anxiety.
In 2012, the FDA cleared QIAGEN’s therascreen KRAS test, which is a genetic test designed to detect the presence of seven mutations in the KRAS gene in colorectal cancer tissue specimens. This test is used to aid physicians in identifying patients with metastatic colorectal cancer for treatment with Erbitux. The presence of KRAS mutations in colorectal cancer tissue indicates that the patient may not benefit from treatment with Erbitux. If the test result indicates that the KRAS mutations are absent in the colorectal cancer cells, then the patient may be considered for treatment with Erbitux.
The Cobas® KRAS Mutation Test is FDA approved for use with the Cobas® 4800 System as a real-time PCR test for the detection of seven somatic mutations in codons 12 and 13 of the KRAS gene in DNA derived from formalin-fixed paraffin-embedded human colorectal cancer (CRC) tumor tissue. The test is intended to be used as an aid in the identification of CRC patients for whom treatment with Erbitux® (cetuximab) or with Vectibix® (panitumumab) may be indicated based on a no mutation detected result. Specimens are processed using the Cobas® DNA Sample Preparation Kit for manual sample preparation and the Cobas z 480 analyzer for automated amplification and detectionU.S. Department of Health and Human Services http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/InVitroDiagnostics/ucm301431.htm.
Liquid Biopsy Tests for KRAS Mutations
Certain fragments of DNA shed by tumors into the bloodstream can potentially be used to noninvasively detect KRAS mutations.
For most tumors, a tissue biopsy is challenging – it is costly, painful, or potentially risky for the patient. Circulating tumor DNA (ctDNA) liquid biopsy enables specific understanding of what kind of molecular changes are happening in the tumor in real time.
In order to address issues associated with tissue biopsy, the use of surrogate sources of DNA, such as blood or urine samples, which contain circulating tumor DNA (ctDNA), has emerged as a new strategy for tumor genotyping.
Today, circulating tumor DNA (ctDNA) may hold benefits that the traditional cancer diagnostic methods or tissue biopsies can’t offer such as detection through urine or blood without an invasive procedure like surgery. The evolution of sensitive ctDNA detection technologies has enabled the development of liquid biopsies with many clinical applications.
Trovagene Precision Cancer Monitoring
The use of Trovagene’s urine or blood liquid biopsy is only intended for detection and monitoring of mutations in patients previously diagnosed with cancer. It is not intended for screening of asymptomatic patients to diagnose cancer.
The Trovera Difference
Trovera liquid biopsy tests provide actionable information about mutations associated with common solid tumor cancers to aid physicians in choosing the right treatment for the right patient at the right time.
Noninvasive identification of clinically actionable mutations to inform treatment decisions.
Highly sensitive analysis of tumor dynamics.
Response to therapy, emergence of resistance mutation(s), disease progression and minimal residual disease.
References [ + ]
|1.||↑||The Genetics of Pancreatic Cancer http://pathology.jhu.edu/pancreas/geneticsweb/K-ras.htm|
|2.||↑||Pancreatic Cancer Action Network https://www.pancan.org/wp-content/uploads/2016/11/2016-GAA-PC-Facts.pdf|
|3.||↑||Medscape Colorectal Cancer and KRAS/BRAF – April 26, 2016 http://emedicine.medscape.com/article/1690010-overview?pa=5Jq32LpUYMFWxC3xr%2B2t15RSYyIhPHSMO7%2Fq%2FNVF1pyQ5JEX7vs%2FxkNm5edN01H6YogTQJgmlryOawBeQxt8WeN5lPYw%2FtQ7Z8WOOzpssmw%3D|
|4.||↑||My Cancer Genome – KRAS in NSCLC https://www.mycancergenome.org/content/disease/lung-cancer/kras/|
|5.||↑||Mayr D, Hirschmann A, Lohrs U, Diebold J: KRAS and BRAF mutations in ovarian tumors: a comprehensive study of invasive carcinomas, borderline tumors and extraovarian implants. GynecolOncol. 2006, 103 (3): 883-887. 10.1016/j.ygyno.2006.05.029.|
|6.||↑||Caduff RF, Svoboda-Newman SM, Ferguson AW, Johnston CM, Frank TS: Comparison of mutations of Ki-RAS and p53 immunoreactivity in borderline and malignant epithelial ovarian tumors. Am J SurgPathol. 1999, 23 (3): 323-328. 10.1097/00000478-199903000-00012.|
|7.||↑||JCO 2015 33 (25) Future Oncol 2015 11(3)|
|8.||↑||U.S. Department of Health and Human Services http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/InVitroDiagnostics/ucm301431.htm|