Who this is for
Stage IV bowel cancer treatment is no longer the same for every patient. Molecular testing, the location of the original tumour and where the cancer has spread can all influence the treatment plan.
This article is for anyone who has recently been diagnosed with bowel cancer that has spread beyond the bowel.
One of the most common questions I hear in my clinic is:
“Doctor, my friend also has stage IV bowel cancer. Why is their treatment completely different from mine?”
It is an excellent question.
The answer reflects one of the biggest changes I have witnessed during my career as a medical oncologist.
A shift in clinical practice
Over the past few months, I have met several patients who reminded me why explaining modern bowel cancer treatment is so important.
One was an 80-year-old lady who had gradually lost weight over several months. She told me she simply did not enjoy food anymore. She also found it increasingly difficult to open her bowels. At first, both she and her family thought these changes were simply part of getting older.
Unfortunately, her CT scan told a different story.
She had bowel cancer that had already spread to her liver.
During another consultation, a patient raised the same concern about why people with the same stage of bowel cancer may receive very different treatments.
Ten or fifteen years ago, the answer might have been relatively simple. Most patients received similar chemotherapy.
Today, modern oncology looks very different.
Looking beyond the CT scan
When I began my oncology training, treatment decisions were largely based on where the cancer had spread and how extensive it appeared on the scan.
Those things still matter.
However, they are no longer the whole story.
Today, before I recommend any treatment, I first want to understand the biology of the cancer.
Two patients may have almost identical CT scans.
Both may have liver metastases.
Both may be the same age.
Yet their best treatment may be completely different.
That is because we are no longer treating bowel cancer as a single disease.
Every cancer has its own fingerprint
One of my first priorities when meeting a patient with stage IV bowel cancer is to ensure that the tumour has undergone the recommended molecular testing.
I often explain it to families like this:
Every cancer has its own fingerprint.
Tests may look for changes called KRAS, NRAS, BRAF, HER2 and MSI or MMR.
You do not need to remember all these names.
What matters is that these results help us understand which treatments are more likely to work and which treatments are unlikely to help.
They allow us to personalise treatment rather than giving every patient the same chemotherapy.
Why the side of the bowel matters
Another important lesson I have learned is that where the cancer started can also influence treatment.
Cancers that begin on the right side of the colon often behave differently from cancers that begin on the left.
This does not mean that one side is always better or worse.
It means that the location of the original cancer, together with its molecular results, can help oncologists choose the most appropriate targeted treatment.
From the pathology report to the treatment plan
When I reviewed the pathology report and CT scans with my 80-year-old patient and her family, we were not simply treating “bowel cancer.”
We were treating her bowel cancer.
Her tumour had started on the right side of the colon.
Molecular testing also showed an NRAS mutation.
Those findings immediately influenced my recommendation.
The NRAS mutation told me that targeted treatments called cetuximab or panitumumab were unlikely to benefit her.
Instead, in her individual situation, the evidence supported considering chemotherapy with bevacizumab.
Bevacizumab is a targeted medicine that blocks signals the cancer uses to form new blood vessels.
This is what precision medicine really means.
It is not about giving the newest drug.
It is not about giving the most expensive drug.
It is about choosing the treatment with the strongest evidence for that particular patient.
Treatment is more than choosing the right drug
Chemotherapy remains an important treatment for many patients with stage IV bowel cancer.
Doctors may combine it with a targeted medicine selected according to the biology of the tumour.
However, not every patient needs chemotherapy first.
Some patients whose cancers are MSI-high or dMMR may receive immunotherapy as their first treatment.
In Australia, the Pharmaceutical Benefits Scheme may subsidise many of these treatments for eligible patients.
For international or self-funded patients, treatment costs can vary significantly.
A treatment plan must not only be scientifically appropriate—it must also be practical and accessible.
Why I am more optimistic today
When I first entered oncology, stage IV bowel cancer often carried very limited expectations.
That is no longer the case.
I still remember a patient who was diagnosed with stage IV bowel cancer more than twenty years ago.
She initially received chemotherapy.
She later underwent surgery to remove cancer from her liver.
Several years afterwards, another small recurrence developed in her lung, which was also successfully removed.
Today, she remains free of cancer.
Will every patient experience that outcome?
Unfortunately not.
However, stories like hers remind me how dramatically bowel cancer treatment has changed.
For carefully selected patients whose cancer has spread to only a limited number of sites, long-term survival—and occasionally the possibility of cure—may be achievable.
That is why every treatment decision deserves careful thought from the very beginning.
What this means for you
If you have recently been diagnosed with stage IV bowel cancer, I encourage you to discuss the following questions with your oncologist.
- Has my tumour undergone recommended molecular testing?
- Does the location of my bowel cancer influence my treatment options?
- Am I suitable for a targeted treatment alongside chemotherapy?
- Will my case be discussed at a multidisciplinary meeting to consider surgery or other local treatments if I respond well?
These questions help ensure that treatment is tailored to your individual cancer rather than following a one-size-fits-all approach.
Key takeaways
- Stage IV bowel cancer is not a single disease. Two patients with the same stage may need very different treatments.
- Molecular testing and the location of the original tumour help oncologists select chemotherapy, targeted treatment or immunotherapy.
- For carefully selected patients, surgery or other treatments directed at liver or lung metastases may offer long-term disease control and, occasionally, the possibility of cure.
The science behind this article
Modern management of metastatic colorectal cancer has evolved from a one-size-fits-all approach to precision medicine. Today, treatment decisions are guided by the biology of the tumour, including molecular markers such as KRAS, NRAS, BRAF, HER2 and MSI, together with the location of the primary tumour within the bowel. These advances allow oncologists to select treatments that are more likely to benefit individual patients while avoiding therapies that are unlikely to be effective.
Key evidence
- Cervantes A, Adam R, Roselló S, et al. Metastatic colorectal cancer: ESMO Clinical Practice Guideline for diagnosis, treatment and follow-up. Ann Oncol. 2023;34(1):10-32. doi:10.1016/j.annonc.2022.10.003
- Bray A, Chang GJ, Ciombor KK, et al. NCCN Clinical Practice Guidelines in Oncology: Colon Cancer. Version 2.2026. National Comprehensive Cancer Network; 2026. Accessed July 22, 2026. https://www.nccn.org/guidelines/guidelines-detail?category=1&id=1428
- Morris VK, Kennedy EB, Baxter NN, et al. Treatment of metastatic colorectal cancer: ASCO guideline. J Clin Oncol. 2023;41(3):678-700. doi:10.1200/JCO.22.01690
- Watanabe J, Muro K, Shitara K, et al. Panitumumab vs bevacizumab added to standard first-line chemotherapy and overall survival among patients with RAS wild-type, left-sided metastatic colorectal cancer: a randomized clinical trial. JAMA. 2023;329(15):1271-1282. doi:10.1001/jama.2023.4428
- André T, Shiu KK, Kim TW, et al. Pembrolizumab versus chemotherapy in microsatellite instability-high or mismatch repair-deficient metastatic colorectal cancer: 5-year follow-up from the randomized phase 3 KEYNOTE-177 study. Ann Oncol. 2025;36(3):277-284. doi:10.1016/j.annonc.2024.11.012
Frequently asked questions (FAQs)
- Why do I need molecular testing?
Because it helps identify treatments that are more likely to work for your particular cancer while avoiding treatments that are unlikely to provide benefit.
- Why does it matter whether the cancer started on the left or right side?
Cancers arising from different parts of the bowel often have different biology and may respond differently to certain targeted treatments.
- Does everyone with stage IV bowel cancer receive chemotherapy?
No. Many patients receive chemotherapy, sometimes combined with a targeted medicine. However, some patients whose cancers are MSI-high or dMMR may receive immunotherapy as their first treatment.
- Can stage IV bowel cancer ever be cured?
For most patients, treatment aims to control the disease for as long as possible while maintaining quality of life. However, in carefully selected patients whose cancer is confined to a limited number of sites, surgery and other local treatments may result in long-term remission and, occasionally, cure.
Dr Dilanka De Silva
MBBS, MRCP(UK), MRCP(UK SCE Oncology), FRACP, PhD
Medical Oncologist & Cancer Genetics Physician
Memorial Sloan Kettering Cancer Center Fellow (New York, USA)