Definition of RAS
The RAS gene family is widely expressed in mammalian cells where encodes four small (21 kDa), cytoplasmic proteins with GTPase activity: H-Ras, K-Ras4a, K-Ras4b, and N-Ras.
They function as molecular switches transducing extracellular stimuli such as mitogens and differentiation factors to transcription factors and cell cycle proteins in the nucleus in order to promote cell growth, differentiation, proliferation and survival.
Extracellular stimuli activate firstly transmembrane tyrosine kinase receptors (RTKs) which recruits adaptor proteins that catalyse the hydrolysis of GDP to GTP on Ras. Once activated, Ras recruits and stimulates number of effectors of complex signalling network pathways including Raf/MEK/ERK mitogen activated protein kinase (MAPK) pathway, the phosphoinositide 3-kinase PI3K/Akt and Ral-GEF proteins.1
Activating mutations in members of RAS family have been found in 20–25% of human cancers. Mutations in RAS are single nucleotide point mutations that more frequently interest the exon 2 codons 12 13 and exon 3 codon 61. These mutations set proteins in a permanently activated state (GTP-bound conformation) impairing the ATPase activity.
Deregulated Ras signalling results in increased proliferation, angiogenesis, and motility, as well as in decreased apoptosis and in altered cellular metabolism.
KRAS is the most commonly mutated isoform in almost 22% of all human cancers, followed by NRAS (8%) and HRAS (3.3%).
Different types of cancer appear to be related to a particular RAS isoform mutation. KRAS mutations are most commonly found in cancers of the pancreas, colon, lung and biliary tract while NRAS mutations are more common in malignant melanoma and haematopoietic system. Lastly HRAS mutations are most common in cancers of the head and neck and urinary tract.1,2
RAS Mutations in Colorectal Cancer
In colorectal cancer KRAS is mutated in approximately 40% of cases mostly in exon 2 codons 12 (70-80%) and 13 (15-20%). The remaining mutations are mainly located in exon 3 codons 59-61 and in exon 4, which includes codons 117 and 146. Mutations in NRAS are present in approximately 3% to 5% of colorectal cancer samples particularly in exon 3 codon 61 (60%) and in exon 2 codons 12, 13.
NRAS mutations are typically mutually exclusive with KRAS mutations. HRAS mutations represent a negligible event.3
Mutations in KRAS are considered an early event in colorectal carcinogenesis and are maintained during the colorectal cancer development, as demonstrated by the highly concordant rate (almost 95%) in paired primary cancers and metastatic samples, except between primary tumours and metastatic lymph nodes.4 Mutations in KRAS or NRAS lead to continuous activation MAPK pathway even if the EGFR is inactivated by drugs.5
RAS as a Prognostic Biomarker in Colorectal Cancer
The prognostic role of RAS mutations in patients with colorectal cancer remains controversial.
A negative effect of KRAS mutations have been reported both in the adjuvant and in metastatic setting but no definitive conclusions have been drawn.6
In a retrospective series of chemo-refractory patients with metastatic colorectal cancer treated with anti-EGFR monoclonal antibodies a poorer median overall survival has been observed in NRAS and KRAS mutated tumours compared to all wild type ones.7
Some authors described a possible negative prognostic role forRASmutations in patients undergoing liver surgery for colorectal cancer metastases, however this data has not been confirmed in a recent series.8
RAS as a Predictive Biomarker in Colorectal Cancer
Several clinical trials highlighted the role KRAS exon 2 (codons 12 and 13) mutations as biomarkers of resistance to anti-EGFR monoclonal antibodies cetuximab and panitumumab.9 De Roock et al. reported longer progression-free survival and overall survival in metastatic colorectal cancer patients carrying a KRAS mutation in codon 13 compared with patients harbouring other KRAS mutations when treated with cetuximab, however this data has not yet been confirmed in prospective clinical trial.10 Recently retrospective and prospective trials have demonstrated the inefficacy of anti-EGFR monoclonal antibodies in metastatic colorectal cancer harbouring either mutations both in KRAS exons 3-4 and in NRAS exons 2-3-4. Sorich and colleagues published a meta-analysis of several randomised controlled trials evaluating EGFR antibodies in different lines of therapy for metastatic colorectal cancer. They found firstly that roughly 20% of KRAS exon 2 wild-type tumours harboured other RAS mutation that impair the effectiveness of anti-EGFR antibodies and secondly confirmed that anti-EGFR antibodies treatment was superior for all–RAS wild-type tumours compared with the expanded RAS mutant subgroup in terms of both progression-free survival and overall survival. Interestingly efficacy was not significantly different between the other RAS mutations and KRAS exon 2–mutant subgroups.11
For this reason the European Medicines Agency has recently updated prescribing indications for panitumumab and cetuximab, restricting their use to the 47% of patients with RAS wild type metastatic colorectal cancer.12,13
RAS Testing Recommendations in Colorectal Cancer
RAS mutation status should be obtained by a validated test carried out in an accredited (certified) institution that includes appropriate quality controls.
Different methods can be used to detect RAS mutations in colorectal cancer specimens, such as mutation-specific real-time polymerase chain reaction (RT-PCR), Sanger sequencing, pyrosequencing, BEAMing technique, next-generation sequencing and dideoxy nucleotide sequencing. There are several manufacturers of targeted genetic tests that can detect RAS mutations in colorectal cancer samples. Tissue materials of either primary or metastatic lesions are applicable for RAS mutation testing since the concordance rate of the mutation status between primary tumours and metastatic sites reached 93%.14
Which Technique and Which Algorithm Should be Used for the Analysis of the RAS Status in Colorectal Cancer?
All methods used to detect RAS mutations have advantages and disadvantages, and the choice to use one over the other is usually based on current local practices and experience in the different clinical laboratories. Parameters that should be considered when choosing a suitable companion diagnostic test include sensitivity, specificity, limit of analytical sensitivity and failure rates.
Methods to increase the sensitivity and specificity and to reduce the failure rates include:
- validating the chosen method thoroughly through comparison with 'gold-standard' methods,
- performing macrodissection of specimens to increase the sensitivity of the technique,
- choosing small amplicons for PCR amplification to reduce the failure rate due to DNA degradation,
- ongoing validation of the method through application of best practice and participation in external quality controls.14
Patient Selection
In line with the clinical practice guidelines of the European Society for Medical Oncology, patients with metastatic colorectal cancer must be screened for RAS mutations before initiating any anti-EGFR therapy since it has been widely demonstrated the ineffectiveness of these treatments in metastatic colorectal cancer harbouring any RAS mutation; it also would avoid drug-induced toxicity and unnecessary cost expenses.15
References
- Prior IA, Lewis PD, Mattos C. A comprehensive survey of Ras mutations in cancer. Cancer Res 2012;72:2457–2467.
- Forbes SA, Bindal N, Bamford S, et al. COSMIC: mining complete cancer genomes in the Catalogue of Somatic Mutations in Cancer. Nucleic Acids Res 2011;39:D945–50.
- JL Bos, ER Fearon, SR Hamilton, et al. Prevalence of ras gene mutations in human colorectal cancers. Nature 1987;327:293–297.
- Han CB, Li F, Ma JT, Zou HW. Concordant KRAS mutations in primary and metastatic colorectal cancer tissue specimens: a meta-analysis and systematic review. Cancer Invest 2012;30:741–747.
- S Benvenuti, A Sartore-Bianchi, F Di Nicolantonio, et al. Oncogenic activation of the RAS/RAF signaling pathway impairs the response of metastatic colorectal cancers to anti-epidermal growth factor receptor antibody therapies, Cancer Res 2007;67:2643–2648.
- T Yokota. “Are KRAS/BRAF Mutations Potent Prognostic And/or Predictive Biomarkers in Colorectal Cancers?” Anti-Cancer Agents in Medicinal Chemistry 2012;12(2):163–171.
- Schirripa M, Cremolini C, Loupakis F, et al. Role of NRAS mutations as prognostic and predictive markers in metastatic colorectal cancer. Int J Cancer 2015;136: 83–90.
- Schirripa M, Bergamo F, Cremolini C, et al. BRAF and RAS mutations as prognostic factors in metastatic colorectal cancer patients undergoing liver resection. British Journal of Cancer 2015;112:1921–1928.
- Vecchione L, Jacobs B, Normanno N, et al. EGFR-targeted therapy. Exp Cell Res 2011;317(19):2765-71.
- De Roock W, Jonker DJ, Di Nicolantonio F,et al. Association of KRAS p.G13D mutation with outcome in patients with chemotherapy-refractory metastatic colorectal cancer treated with cetuximab, JAMA 2010;304(16):1812–1820.
- Sorich MJ, Wiese MD, Rowland A,et al. Extended RAS mutations and anti-EGFR monoclonal antibody survival benefit in metastatic colorectal cancer: a meta-analysis of randomized, controlled trials. Ann Oncol 2015;26(1):13-21.
- European Medicines Agency, Committee for Medicinal Products for Human Use. Erbitux Assessment report EMA/CHMP/701107/2013.
- European Medicines Agency, Committee for Medicinal Products for Human Use. Vectibix Assessment report EMA/413562/2013.
- Wong N, Gonzalez D, Salto-Tellez M, et al. RAS testing of colorectal carcinoma – a guidance document from the association of clinical pathologists molecular pathology and diagnostics group. J Clin Pathol 2014;67: 751–757.
- Van Cutsem E, Cervantes A, Nordlinger B, et al. Metastatic colorectal cancer: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. Ann Oncol (2014) 25 (suppl 3): iii1-iii9.
FAQs
What is the RAS mutation in colorectal cancer? ›
Mutations in RAS are single nucleotide point mutations that more frequently interest the exon 2 codons 12 13 and exon 3 codon 61. These mutations set proteins in a permanently activated state (GTP-bound conformation) impairing the ATPase activity.
Which ras gene mutation is most common in colorectal cancer? ›KRAS is the most frequently mutated of the three Ras isoforms in 19 of the 29 cancer types in Table 1 and is responsible for 75% of Ras-mutant cancers.
What are potential biomarkers for colorectal cancer? ›Methylated genes such as MLH1, VIM and SEPT9, could be used as biomarkers for colorectal cancer and as DNA-based colon cancer screening tests. Methylated Vimentin (mVim) is a validated stool-based biomarker for early detection of colorectal cancer available in the US (ColoGuard assay; LabCorp)[48].
How is RAS mutated colorectal cancer treated? ›Current treatment for RAS-mutant metastatic CRC is primarily based on combinations of 5-fluorouracil with oxaliplatin or irinotecan and antiangiogenic agents bevacizumab and aflibercept in the first- and second-line settings.
What mutation is commonly found in Ras genes in cancer cells? ›Ras mutations
Specific mutations at codons 12, 13, or 61 in the Ras genes is associated with tumors. Those mutations favor constitutive activation of Ras, meaning that the gene is always “turned on,” and there is overproduction of the protein. The mutation also increases GTP binding, leading to overactivity.
The Problem with RAS Genes
It has been known for more than three decades that about a third of all human cancers, including a high percentage of pancreatic, lung, and colorectal cancers, are driven by mutations in RAS genes.
The COSMIC dataset confirms that K-Ras is the most frequently mutated isoform present in 22% of all tumours analysed compared to 8% for N-Ras and 3% for H-Ras (Table 1).
How many Ras mutations are there? ›Forty-four separate point mutations have been characterized in Ras isoforms, with 99.2% of all mutations occurring at codons 12, 13, and 61.
Is KRAS a Ras mutation? ›KRAS is the most commonly mutated member of the RAS family and is considered to be the most common oncogenic gene driver in human cancers58,59. KRAS mutations are most common in PDAC, CRC, and NSCLC.
What is the best marker for colorectal cancer? ›Carcinoembryonic antigen (CEA) level: The tumor marker most often used in colorectal cancer. This level can be checked before surgery to predict prognosis, can be used during therapy to watch response to treatment, or when you are done treatment to watch for recurrence.
What is the best tumor marker for colorectal cancer? ›
CEA is a glycoprotein which is formed in the cells of the large bowel. Seventy percent of patients with CRC have high CEA levels during diagnosis, which makes it a very good marker for the treatment and monitoring of the disease after resection.
What are the prognosis biomarkers for colorectal cancer? ›Biomarkers include DNA, proteins, and genetic mutations found in blood, tissue, or other body fluids. Your “biomarker profile” can help you and your doctor personalize your treatment. Biomarkers for colorectal cancer are used for diagnosis, progression, prognosis, and for treatment.
What deactivates RAS? ›RAS is activated by GDP/GTP exchange stimulated by GEFs and inactivated by GTP hydrolysis stimulated by GAPs. The very slow off-rate for GDP (t1/2 = 6 min, koff = 2 × 10−3 s−1 at 20°) (Hunter et al., 2015) allows RAS proteins to remain in their inactive states until signals provoke GDP/GTP exchange.
Is RAS a tumor suppressor gene? ›The Ras Effector RASSF2 Is a Novel Tumor-Suppressor Gene in Human Colorectal Cancer.
Do patients with colon cancer often have a mutation in the KRAS RAS gene? ›The RAS gene family is among the most studied and best characterized of the known cancer-related genes. Of the three human ras isoforms, KRAS is the most frequently altered gene, with mutations occurring in 17%–25% of all cancers. Particularly, approximately 30%–40% of colon cancers carry a KRAS mutation.
What's the difference between KRAS and Ras? ›The mutations rates at each codon differ between the RAS proteins (2). While KRAS is commonly mutated at codon 12 with only few mutations occurring at codon 61, NRAS mutations are most frequently observed at codon 61.
Is Ras mutation dominant? ›The use of the dominant negative mutant of Ras has been crucial in elucidating the cellular signaling of Ras in response to the activation of various membrane-bound receptors.
Is Ras mutation inherited? ›Mutations in N-RAS genes are generally somatic and not inherited.
What would happen if a cell contained a mutant RAS protein that was in a permanently on state? ›Mutations in Ras genes can lead to the production of permanently activated Ras proteins, which can cause unintended and overactive signaling inside the cell, even in the absence of incoming signals. Because these signals result in cell growth and division, overactive Ras signaling can ultimately lead to cancer.
What diseases have RAS mutations? ›RAS mutations are highly prevalent in hematologic malignancies including chronic and juvenile myelomonocytic leukemia (CMML and JMML), acute myeloid leukemia (AML), acute lymphocytic leukemia (ALL) and multiple myeloma (MM).
Where do RAS mutations occur? ›
Mutant forms of RAS are common in lung and colorectal cancers and are present in almost 95 percent of pancreatic cancers.
Why is it difficult to target Ras? ›This is due to the relative cellular abundance of GTP, and the binding affinity of RAS for GTP being extremely high. There's also an apparent lack of suitable surfaces in critical regions of RAS proteins necessary for small-molecules to bind, making tumors bearing these mutations among the most difficult to treat.
What is the most common KRAS mutation? ›In this study, they reveal that KRAS mutations were always found to involve codon 12, with KRAS G12C being the most frequently found (63.6%).
What can result from an always activated Ras protein? ›Cancer-causing mutation of Ras creates a form of the protein that is always on. This is a disaster, because the mutated Ras continually tells the cancer cells that it is okay to multiply, without the normal limits that control cell growth.
What are the hotspots of RAS mutations? ›Approximately 94% of RAS mutations occur at one of three mutational "hot spots" at Gly12, Gly13 and Gln61.
How do you test for RAS mutation? ›RAS mutation detection in routine clinical practice is usually performed using DNA extracted from formalin-fixed paraffin embedded (FFPE) tumor specimens [6].
What are the three isoforms of RAS? ›Ras are small cellular GTPases which regulate diverse cellular processes. It has three isoforms: H-Ras, K-Ras, and N-Ras.
Is KRAS mutation aggressive? ›Abstract: Metastatic colorectal cancer (CRC) is a topic of intense research. KRAS mutations have emerged as aggressive drivers of disease.
Is KRAS a biomarker? ›KRAS is an important biomarker that can impact lung what treatment options. Talk to your doctor about comprehensive biomarker testing.
What drugs target KRAS? ›Last year, FDA approved the first KRAS inhibitor, sotorasib, to treat people with non-small cell lung cancer that has this specific KRAS mutation. Several other KRAS G12C inhibitors are being tested in late-stage clinical trials. Not all tumors with a KRAS G12C mutation respond to these drugs, however.
What is a high CEA level for stage 4 colon cancer? ›
For example, those with stage 3 colon cancer have CEA at 5 ng/mL or less, while patients with stage 4 colon cancer tested more than 5 ng/mL. CEA levels that are extremely elevated, such as going as high as 20 ng/mL, could suggest that cancer has started to spread to other tissues – a process called metastasis.
What is a high CA 15-3 level? ›CA 15-3 levels and normal range
The normal range for a healthy person is 30 U/mL or less. Further testing is recommended if CA 15-3 levels are above the normal range. According to the National Institutes of Health, CA 15-3 levels are elevated in approximately 76 percent of metastatic breast cancer cases.
It's most commonly used in colorectal cancer. A provider may order a CEA test along with other tests to: Learn more about a cancer soon after it has been diagnosed. CEA levels can help predict the likelihood of recovery and/or the chance that cancer will come back after treatment.
What is the strongest prognostic factor in colorectal cancer? ›Stage. Stage is the most important prognostic factor for colorectal cancer. The lower the stage at diagnosis, the better the outcome.
What are colorectal cancer blood markers? ›Tumor marker tests are used to check for two substances in the blood that colorectal cancer may produce: carcinoembryonic antigen (CEA) and CA 19-9. The tests may help determine an appropriate course of treatment and, sometimes, whether the disease is likely to recur.
What are the colorectal cancer stem cell biomarkers? ›There are distinct subpopulations of cells within a tumor that express different combinations of stem cell markers and have different functions. The following markers are typically considered as markers of colorectal adenocarcinoma stem cells: CD133, CD144, CD24, CD166, CD44, CD29, ALDH1, LGR5, and CXCR4.
What happens if Ras is always on? ›These mutations result in a K-Ras protein that is constantly turned on (constitutively activated) and directing cells to proliferate in an uncontrolled way, which leads to tumor formation. When these genetic changes occur in cells in the lungs, lung cancer can develop.
What is Ras and why is it important in many cancers? ›Ras gene mutation has been observed in more than 30% of cancers, and 90% of pancreatic, lung and colon cancers. Ras proteins (K-Ras, H-Ras, N-Ras) act as molecular switches which are activated by binding to GTP. They play a role in the cascade of cell process control (proliferation and cell division).
What happens when Ras is inhibited? ›Blocking the RAS pathway will likely lead to the emergence of drug resistance due to feedback reactivation of the ERK and PI3K pathways by receptor tyrosine kinases, secondary KRAS mutations or amplification in downstream RAS effectors (56).
How does Ras get activated? ›After growth factor stimulation, the tyrosine phosphorylated EGF receptor binds the Grb2/Sos complex, translocating it to the plasma membrane. This translocation is thought to bring Sos into close proximity with Ras, leading to the activation of Ras.
What happens when Ras becomes an oncogene? ›
Oncogenic mutations in the RAS genes, which create constitutively-active Ras proteins, can result in uncontrolled proliferation or survival in tumor cells.
Is RAS gene dominant or recessive? ›Because this type of mutation makes a gene product hyperactive, the effect is dominant—only one of the cell's two gene copies needs to undergo the change. The Ras genes are mutated in a wide range of human cancers, and they remain one of the most important examples of cancer-critical genes.
What mutations of RAS is most likely associated with cancer? ›KRAS is the most frequently mutated of the three Ras isoforms in 19 of the 29 cancer types in Table 1 and is responsible for 75% of Ras-mutant cancers.
What percent of cancers show mutations to RAS? ›RAS mutations (HRAS, NRAS, and KRAS) are among the most common oncogenes, and around 19% of patients with cancer harbor RAS mutations.
What is the RAS mutation? ›A family of genes that make proteins involved in cell signaling pathways that control cell growth and cell death. Mutated (changed) forms of the RAS gene may be found in some types of cancer. These changes may cause cancer cells to grow and spread in the body.
Is KRAS a RAS mutation? ›KRAS is the most commonly mutated member of the RAS family and is considered to be the most common oncogenic gene driver in human cancers58,59. KRAS mutations are most common in PDAC, CRC, and NSCLC.
What does RAS gene stand for? ›RAS is an abbreviation of “Rat sarcoma,” reflecting how the first members of the RAS gene family were discovered over three decades ago. The RAS family is composed of 36 human genes, but KRAS, NRAS, and HRAS by far play the most prominent roles in human cancer (1).
Which of the RAS proteins is the most mutated in cancers? ›The COSMIC dataset confirms that K-Ras is the most frequently mutated isoform present in 22% of all tumours analysed compared to 8% for N-Ras and 3% for H-Ras (Table 1).
What is the most common type of mutation in the RAS gene? ›The RAS gene isoforms are also distinguished by their striking differences in the mutation frequency at each of the three hotspots (G12, G13 and Q61) (see poster). G12 mutations comprise 83% of all KRAS mutations, followed by G13 mutations (14%), whereas Q61 mutations are rare (2%).
How many RAS mutations are there? ›Forty-four separate point mutations have been characterized in Ras isoforms, with 99.2% of all mutations occurring at codons 12, 13, and 61.
What is the difference between KRAS and Ras? ›
The mutations rates at each codon differ between the RAS proteins (2). While KRAS is commonly mutated at codon 12 with only few mutations occurring at codon 61, NRAS mutations are most frequently observed at codon 61.
Is KRAS and Ras the same thing? ›The KRAS gene is in the Ras family of oncogenes, which also includes two other genes: HRAS and NRAS. These proteins play important roles in cell division, cell differentiation, and the self-destruction of cells (apoptosis).