Personalised Medicine: Understanding Biomarker Testing in Bowel Cancer

In recent years, bowel cancer treatment in Australia has entered a new era, one where science is not only advancing rapidly, but also becoming more personal. At the heart of this evolution is biomarker testing, a tool that’s helping oncologists tailor treatment to the unique biology of each individual’s cancer. This shift from a “one-size-fits-all” approach to personalised medicine has the potential to dramatically improve outcomes, especially for those diagnosed with early-onset bowel cancer.

Understanding what biomarker testing involves, why it matters, and how it can shape your treatment plan is a key step in becoming an informed and empowered patient. Here’s what you need to know.

What Is Personalised Medicine?

Personalised medicine, also known as precision medicine, refers to medical care that’s customised based on an individual’s specific genetic, molecular, and environmental profile. For cancer patients, this means treatment plans that consider the unique characteristics of the tumour, not just its location or size, but the specific genetic mutations or biomarkers that are driving its growth.

This is particularly important in bowel cancer, where a growing list of biomarkers can now be tested to help determine the most effective treatment options and avoid those that are unlikely to work.

What Are Biomarkers?

Biomarkers are biological indicators, molecules found in tissue, blood, or other body fluids, that provide information about what’s happening in the body. In the context of bowel cancer, biomarkers can reveal:

• How aggressive the cancer is
• Whether the cancer is likely to respond to certain treatments
• The likelihood of the cancer returning after treatment
• If there are inherited mutations that may affect family members

Biomarkers can be genetic (inherited or acquired mutations), protein-based, or related to how the immune system is interacting with the cancer. Testing for these biomarkers is what allows doctors to match patients with the therapies most likely to work for their specific tumour type.

Common Biomarkers in Bowel Cancer

In Australia, oncologists often test for a set of key biomarkers in bowel cancer patients, particularly those with metastatic or recurrent disease. For early-onset cases, biomarker testing is increasingly being offered at diagnosis due to the growing understanding that these cancers may behave differently.

Here are the most commonly tested biomarkers in bowel cancer:

• RAS mutations (KRAS and NRAS)
  These mutations affect signalling pathways that control cell growth. If a tumour has a RAS mutation, EGFR inhibitor therapies like cetuximab and panitumumab are unlikely to work.
• BRAF V600E mutation
  Found in around 10% of colorectal cancers, this mutation is associated with a more aggressive cancer type. However, it may respond well to a combination of BRAF inhibitors and other targeted therapies.
• Microsatellite Instability (MSI) / Mismatch Repair Deficiency (dMMR)
  MSI-high or dMMR tumours are less likely to respond to chemotherapy but more likely to respond to immunotherapy like PD-1 checkpoint inhibitors (e.g., pembrolizumab). This testing can also flag the possibility of Lynch syndrome, an inherited condition.
• HER2 amplification
  Though more commonly associated with breast cancer, some bowel cancers overexpress HER2 and may benefit from HER2-targeted therapies.
• NTRK gene fusions
  Rare but clinically significant, these gene fusions can make tumours responsive to highly specific targeted therapies like larotrectinib or entrectinib.
• Tumour Mutational Burden (TMB)
  A high TMB may predict responsiveness to immunotherapy. This test is still gaining traction in standard care but may be relevant in certain clinical trial settings.

Why Biomarker Testing Matters

Biomarker testing in bowel cancer isn’t just a scientific curiosity, it has real-world implications that could directly impact your treatment journey:

• Avoid ineffective treatments: Knowing your biomarker status can help you skip treatments that are unlikely to work, sparing you the side effects and delays.
• Access targeted therapies: Some biomarkers unlock access to highly targeted drugs, which can be more effective and often have fewer side effects than traditional chemotherapy.
• Inform genetic counselling: For example, MSI or dMMR testing can identify patients at risk for Lynch syndrome, a condition that increases the risk for multiple cancers and may affect family members.
• Open clinical trial opportunities: Having detailed biomarker information may qualify you for trials testing cutting-edge treatments in Australia or internationally.

When Is Biomarker Testing Done?

In Australia, biomarker testing is generally recommended in the following situations:

• At diagnosis of stage IV or advanced bowel cancer
• For early-onset bowel cancer, even if non-metastatic, particularly where there is a strong family history or unusual tumour characteristics
• When cancer returns after initial treatment
• Before starting second-line treatments or considering immunotherapy or targeted therapy options

Testing is done on tumour tissue, usually from a biopsy or during surgery. In some cases, liquid biopsy (a blood test) can also be used, especially for monitoring known mutations or when tissue samples are difficult to obtain.

How to Access Biomarker Testing in Australia

While public and private healthcare systems in Australia offer access to many biomarker tests, not all tests are covered by Medicare. This can create challenges, especially for younger patients who may not meet typical criteria for testing or whose cancer is not yet advanced.

Steps to access testing:

• Speak to your oncologist or multidisciplinary team about whether biomarker testing is recommended in your case.
• Ask whether testing will impact treatment options or eligibility for clinical trials.
• Request genetic counselling, especially if your results may suggest an inherited condition like Lynch syndrome.
• Check coverage and costs, as some tests (e.g., BRAF, MSI) are Medicare-funded, while others may need to be self-funded or covered through private health insurance or clinical trials.

Bowel Cancer Australia provides support and information to help patients understand biomarker testing and navigate access pathways. They also advocate for better funding and inclusion of biomarker tests in national guidelines.

Personalised Treatment Pathways

Once biomarker results are available, your care team can create a personalised treatment plan, which may include:

• Chemotherapy combinations tailored to your cancer’s sensitivity
• Targeted therapies, which block specific proteins or genetic pathways
• Immunotherapy, which harnesses your immune system to attack the cancer
• Surgical options for those with specific mutations linked to better outcomes
• Clinical trials offering early access to promising new treatments

For patients with early-onset bowel cancer, personalised approaches are especially important. This age group tends to present with distinct tumour biology, and biomarker testing can uncover options that wouldn’t have been considered under standard protocols.

Personally, I wasn’t offered biomarker testing at diagnosis, but it’s something I’ll be looking into if my cancer progresses. If you’re in a similar boat, it’s worth raising with your team early.

The Role of Genetic Testing

While biomarker testing is focused on the tumour itself, genetic testing looks at your inherited DNA to identify germline mutations that may have contributed to the cancer. If you’re under 50 and diagnosed with bowel cancer, genetic testing is often recommended to rule out hereditary syndromes like:

• Lynch syndrome
• Familial Adenomatous Polyposis (FAP)
• MUTYH-associated polyposis (MAP)

These conditions may not only influence your treatment but also impact screening and prevention plans for your family. Your GP or oncologist can refer you to a familial cancer centre or genetic counsellor to explore this further.

Questions to Ask Your Oncologist

Being proactive in your care means asking the right questions. Here are some to consider:

• Have biomarker tests been done on my tumour?
• What were the results, and how do they affect my treatment options?
• Are there any targeted therapies or immunotherapies that might work for me?
• Should I be referred for genetic counselling?
• Am I eligible for any clinical trials based on my biomarker profile?
• Will I need re-testing if my cancer returns or changes?

Challenges and Limitations

While biomarker testing is a major step forward, it’s not perfect. Limitations include:

• Access and equity issues, especially for rural and regional patients
• Delays in results, which can hold up treatment decisions
• Costs for non-Medicare funded tests, which may place a financial burden on patients
• Unclear results, or results that don’t immediately point to a treatment option

Despite these challenges, testing is a critical tool for navigating treatment more confidently and strategically.

Looking Ahead

Biomarker testing is likely to become standard practice for all bowel cancer patients in the near future. Research continues to identify new markers and develop therapies tailored to them. As technology improves and more data becomes available, Australians, especially those diagnosed young, can expect more refined and personalised care.

Keeping up with this evolving landscape is important, and Bowel Cancer Australia remains a leading source of support and advocacy in this space. They provide resources, helplines, and updates on access pathways to ensure patients can make informed decisions.

Final Thought

Biomarker testing can feel like just another item on a long to-do list after diagnosis, but it could be the key to unlocking treatments that actually work for your specific cancer. If you haven’t had this conversation with your team yet, it’s worth raising. The more we tailor treatment, the more power we take back from this disease.