Colorectal Cancer (CRC) Molecular Biomarkers
International guidelines recommend testing for hotspot mutations in the rat sarcoma viral oncogene homolog (RAS) gene family, including the Kirsten RAS (KRAS) and neuroblastoma RAS (NRAS) proto-oncogenes, to exclude RAS mutation-positive metastatic colorectal cancer (mCRC) patients from receiving anti-epidermal growth factor receptor (EGFR) therapy.
This is because anti-EGFR agents do not provide meaningful survival benefits versus anti-angiogenic/chemotherapy regimens in mCRC patients whose tumours are not wild type (WT) with respect to RAS genes 1,2.
Mutations in proto-oncogene, KRAS, are detected in up to 40% of CRC patients. The activated KRAS gene contributes significantly to several aspects of the tumour growth, including tumour survival, angiogenesis, proliferation and metastasis. It is therefore vital that the KRAS mutation status of a patient’s colorectal tumour can be detected to allow patients access to treatment for which there is an increased likelihood
of benefit 3.
BRAF mutations occur in 15% of colorectal cancers. BRAF mutational status is used as a strong predictor for overall survival (OS) at all stages of disease; patients with BRAF-mutated CRC have a generally poor prognosis.
Traditionally, formalin-fixed paraffin-embedded (FFPE) tumour samples have been used to determine the RAS mutation status of CRC patients in routine clinical practice.
References:
1. Bos JL et al., (1987) Nature 327(6120):293–297.
2. Van Cutsem E et al., (2009) N Engl J Med 360(14):1408–1417
3. Bokemeyer C et al., (2009) J Clin Oncol 27(5):663–671.
Somatic Mutation | Solid Tissue Molecular Profiling in Colorectal Cancer
Colorectal Cancer Solid Tissue Gene Panel
Mutations in proto-oncogene KRAS are detected in up to 40% of CRC1, which can confer resistance to treatment with EGFR antibodies, and only patients with wild-type KRAS tumours obtain benefit from these agents2,3. It is, therefore, vital that the KRAS mutation status of a patient’s colorectal tumour can be detected to allow patients access to treatment.
Genes sequenced in this panel include:
| KRAS | PIK3CA |
| NRAS | PTEN |
| BRAF | AKT1 |
When to Order: At diagnosis for treatment selection.
How to Order: Fill out our Somatic Mutation testing request form and tick the Somatic Mutation test panel required.
Turnaround Time: 5–7 business days from the sample receipt date.
Specimen Required: Fresh formalin-fixed paraffin-embedded (FFPE) of 5-10 μm thickness from the tumour tissue.
Test Cost: Medicare rebate available if criteria is met. If criteria is not met there is an out-of-pocket fee of $400.
A negative result does not rule out the presence of a mutation that may be present but below the limits of detection for this assay (<5%).
References
1. Bos JL et al., (1987) Nature 327(6120):293–297
2. Van Cutsem E et al., (2009) N Engl J Med 360(14):1408–1417.
3. Bokemeyer C et al., (2009) J Clin Oncol 27(5):663–671.
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Aspect ctDNA Liquid Biopsy in Colorectal Cancer
In colorectal cancer, ctDNA could also be used to track clonal evolution and targeted drug responses 1,2.
In patients with metastatic colorectal cancer who developed resistance to EGFR antibodies, analysis of ctDNA identified the emergence of polyclonal and heterogeneous patterns of mutation in KRAS, NRAS, BRAF, or EGFR with mutations found in 96% of panitumumab- or cetuximab refractory patients. Subsequently, Misale et al. were able to illustrate a way to use this information to overcome treatment resistance 3,4,5.
Furthermore, studies demonstrate better outcomes when no tumour-derived DNA is found in patients following surgery or chemotherapy in colorectal cancer patients, whereas those with whom tumour DNA is still present do better with the addition of more aggressive and targeted treatment or chemotherapy 6.
Colorectal Cancer ctDNA Gene Panel
The Aspect Liquid Biopsy colorectal cancer (CRC) ctDNA gene panel can detect DNA alterations in patients’ plasma that guide treatment decisions as detailed below.
Gene panel includes:
- KRAS: 48 mutations across exon 2, 3 and 4
- NRAS: 40 mutations across exon 2, 3 and 4
- BRAF: 5 mutations across exon 11 and 15
- PIK3CA: 4 mutations across exon 9 and 20
- EGFR (T790M NOT included): 10 extracellular mutations across exon 12
When to Order: At diagnosis or to monitor treatment resistance or early relapse.
How to Order: Health practitioners can order Aspect Liquid Biopsy for cancer patients using the Aspect Liquid Biopsy request form.
Turnaround Time: 5–7 business days from the sample receipt date.
Specimen Required: This test requires TWO 10ml blood samples (special tubes), which can be taken at any of our collection centres.
Test Cost: No Medicare rebate available. An out-of-pocket fee of $550 applies.
A negative result does not rule out the presence of a mutation that may be present but below the limits of detection for this assay (<2%).
References:
1. Gray E et al., (2015) Oncotarget 6 (39):42008–42018.
2. Girotti M et al., (2016) Cancer Discov 6 (3):286–299.
3. Bettegowda C et al., (2014) Sci Transl Med 6:224ra24.
4. Misale S et al., (2012) Nature 486(7404):532–536.
5. Misale S et al., (2014) Sci Transl Med 6:224ra26.
6. Tie J et al., (2016) Sci Transl Med 8:346ra92.
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The content on our Molecular Cancer Services page is written by Associate Professor Mirette Saad, National Director of Molecular Genetics at Australian Clinical Labs.
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Assoc. Prof. Mirette SaadMBBS (Hons), MD, MAACB, FRCPA, PhD |
Associate Professor Mirette Saad is a Consultant Chemical Pathologist and the National Director of Molecular Genetics at Australian Clinical Labs. She has a Fellowship with honours in Chemical and Molecular Pathology, with Microbiology sub-speciality, from Suez Canal University, Egypt. A/P Saad received her NHMRC sponsored PhD degree in Cancer Genetics from Melbourne University and Peter MacCallum Cancer Institute. Along with her teaching and research roles, A/P Saad is a registered medical practitioner with AHPRA, a Chemical Pathology Fellow (FRCPA) at the Royal College of Pathologists of Australasia and a Member of the Australasian Association of Clinical Biochemists (MAACB). She is a Chair of the RCPA Chemical Pathology Advisory Committee, Member of the RCPA Genetic Advisory Committee, AACB and a Chair of the Precision Medicine Services at Australian Clinical Labs. At Clinical Labs, A/Prof Mirette Saad leads the Molecular Genetic testing for non-invasive prenatal testing (NIPT), antenatal screening, personalised drug therapy and cancer.