BREAKING BRAF
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Biomarkers
What is a Biomarker? What does it mean? How do they relate to me and my cancer?
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​There are lots of complex words and concepts in the medical world and this can be very alienating and confusing to patients and carers. Read our bite size guide to biomarkers to understand what these are and why they matter when you have a BRAF mutation.
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What is a Biomarker?
A biomarker is something that can be measured to assess a person’s health. The presence or absence of biomarkers, or high or low levels, can be a sign of disease. For cancers, the biomarkers used are molecules related to genes and proteins.
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Biomarkers provide doctors with information to help diagnose different types of cancer and decide on treatment plans, including suitability of clinical trials. These measurements can also help doctors to determine how people are responding to treatment.
What are BRAF Biomarkers?
When the BRAF gene mutates, it can be one of many types. The type of BRAF gene mutation will be noted in your medical records. This will be a series of letters and numbers.
These letters and numbers describe the nature and location of the mutation. By far the most common type of BRAF mutation is V600E -the letters and numbers tells us that valine (V) has been replaced by glutamic acid (E). and the number (600) indicates where the mutation has occurred.
V600E means that the 600th amino acid in the BRAF protein is usually valine, but the mutation means this has been replaced by glutamic acid.
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Your BRAF mutation, alongside any others, will determine which types of treatments may be most suitable for you.
What is Microsatellite status?
Your Oncologist, a Specialist Cancer Doctor, might have spoken to you about your Microsatellite status or you may have seen or heard the letters MSS or MSI-High in relation to your cancer. Microsatellite status is a KEY factor in what treatment you have for BRAF-mutated bowel cancer.
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Microsatellite status describes sections of short, repetitive DNA sequences within the tumour cells. It will be described as either MSS (microsatellite stable) or MSI-High (microsatellite instability).
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Every time a cell divides it makes new copies of these DNA sections. In normal cells, mismatch repair (MMR) proteins spot mistakes in these copies and correct them. However, sometimes the MMR proteins don’t work as they should. This is known as MMR deficiency or dMMR. This is common in people with MSI-High status.
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In summary:
MSS (microsatellite stability) describes normal, stable microsatellites and functioning DNA mismatch repair (pMMR)
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MSI-High (microsatellite instability) describes unstable microsatellites, usually due to deficiency in DNA mismatch repair function (dMMR)
These two types of BRAF bowel cancer are treated very differently, as MSI-High responds well to immunotherapy and has generally better prognosis.
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