Who this is for
Stage II colon cancer chemotherapy is not routinely needed for every patient after surgery. The decision depends on the pathology findings, MMR or MSI status and the expected benefit of treatment.
This article is for people who have had surgery for colon cancer and were told:
- The cancer had grown through the muscular wall of the bowel into the surrounding tissue.
- Doctors classified the cancer as T3.
- All examined lymph nodes were negative.
- Their surgeon has referred them to a medical oncologist to discuss whether chemotherapy is necessary.
Clinical observation
One of the most common referrals I receive is a patient who has undergone an excellent operation for colon cancer.
The pathology report may show:
- T3 colon cancer
- 16 lymph nodes examined
- The pathologist found no cancer in the lymph nodes
- Clear surgical margins
The patient is understandably confused.
“Doctor, if the cancer has been completely removed, why do I need to see an oncologist?”
Many patients expect that I will automatically recommend chemotherapy.
In reality, one of the most important parts of my job is deciding who is likely to benefit from chemotherapy—and who may reasonably be managed without it.
What surprised me
Early in my oncology career, I was surprised by two things.
The first was how small the average benefit of chemotherapy can be for many patients with low-risk stage II colon cancer.
Clinical trials have shown that chemotherapy can reduce the relative risk of recurrence and death. However, because many patients remain cancer-free after surgery alone, the actual additional benefit for an individual patient may be only a few percentage points.
The second surprise was how many patients believe that chemotherapy given through a drip must be stronger than chemotherapy taken as a tablet.
That is not necessarily true.
Capecitabine is an oral chemotherapy medicine. Once inside the body, it is converted into 5-fluorouracil, commonly called 5-FU.
The fact that capecitabine is taken as a tablet does not make it a weaker form of chemotherapy.
Why this matters
The decision about chemotherapy after stage II colon cancer surgery is not simply:
“Was the cancer removed?”
The more useful questions are:
- How deeply had the cancer grown?
- Were enough lymph nodes examined?
- Were the surgical margins clear?
- Were any high-risk features present?
- What was the tumour’s MMR or MSI result?
- How large is the likely benefit of chemotherapy?
- What are the possible short- and long-term side effects?
For some patients, chemotherapy provides a worthwhile additional benefit.
For others, the likely benefit may be too small to justify the risks and inconvenience of treatment.
Understanding the background
What does T3N0 mean?
The bowel wall has several layers.
A T3 tumour has grown through the muscular wall of the bowel and into the surrounding tissue or fat.
N0 means that no cancer was found in the nearby lymph nodes that were examined.
A T3N0 colon cancer is generally classified as stage IIA colon cancer, provided there is no distant spread.
This means the cancer has grown beyond the muscle of the bowel but has not been found in the lymph nodes or distant organs.
Why does the number of lymph nodes matter?
Examining the lymph nodes helps determine whether the cancer has spread beyond the bowel.
Current guidance considers an examination of fewer than 12 lymph nodes to be a high-risk feature because too few nodes may make the staging less certain.
In this example, 16 lymph nodes were examined and all were negative.
This gives us greater confidence that the cancer was correctly classified as node-negative.
However, the number of lymph nodes is only one part of the decision.
What makes stage II colon cancer higher risk?
Important high-risk features include:
- T4 disease
- Fewer than 12 lymph nodes examined
- Bowel obstruction
- Bowel perforation
- Cancer cells seen within blood vessels or lymphatic channels
- Cancer cells growing around nerves
- Poorly differentiated or undifferentiated tumour cells
- A high level of tumour budding—small groups of cancer cells seen at the edge of the tumour
A positive surgical margin is a separate and important concern because it may mean that cancer cells were present at the cut edge of the removed tissue. This requires careful specialist review.
Patients with T3N0 disease and none of these adverse features are generally considered to have lower-risk stage II colon cancer.
One of the most important results: MMR or MSI
Before deciding about chemotherapy, I would also want to review the tumour’s mismatch repair status.
Different pathology reports may use different terms to describe the same result:
- pMMR or MSS means that the tumour’s DNA repair system appears to be working normally.
- dMMR or MSI-high means that part of the tumour’s DNA repair system is not working properly.
These tests examine the tumour’s ability to repair mistakes in its DNA.
In many patients with stage II colon cancer, dMMR or MSI-high status is associated with a lower risk of recurrence. However, the overall risk still depends on the T stage and other pathological features.
Importantly, fluoropyrimidine chemotherapy alone—such as capecitabine or 5-FU—is not routinely recommended for patients with dMMR or MSI-high stage II disease.
This is why the MMR or MSI result is an important part of the chemotherapy discussion.
How was the QUASAR study conducted?
Study
QUASAR trial
Journal
The Lancet
Participants
3,239 patients with colorectal cancer for whom the benefit of chemotherapy after surgery was uncertain
Population
Most participants had stage II colorectal cancer.
Comparison
- Surgery followed by observation
- Surgery followed by fluoropyrimidine chemotherapy
What Did the Researchers Measure?
- Cancer recurrence
- Overall survival
Key results
The QUASAR trial found that chemotherapy was associated with:
- An approximately 18% relative reduction in the risk of death
- An approximately 22% relative reduction in the risk of recurrence
- An estimated absolute improvement in five-year survival of approximately 3.6 percentage points for stage II disease
These numbers require careful explanation.
An 18% relative reduction does not mean that every patient gains an 18% improvement in survival.
Because the chance of cure after surgery is already relatively high for many patients with stage II disease, the actual additional benefit from chemotherapy is much smaller.
The investigators estimated that, among 100 patients similar to those included in the trial, chemotherapy might result in approximately three to four additional patients being alive at five years. This is an average estimate, not a prediction for an individual patient.
The benefit for an individual patient may be smaller or larger depending on the tumour’s pathological and molecular features.
What did the QUASAR trial teach us?
The QUASAR trial did not prove that every patient with stage II colon cancer should receive chemotherapy.
Instead, it showed that fluoropyrimidine chemotherapy can provide a small average benefit.
The decision therefore requires a balance between:
- The estimated risk of the cancer returning
- The likely size of the chemotherapy benefit
- The patient’s age and general health
- MMR or MSI status
- Possible treatment side effects
- The patient’s preferences
This is why chemotherapy is recommended selectively rather than automatically for every patient with stage II colon cancer.
Why don’t we give everyone oxaliplatin?
Many patients ask:
“If chemotherapy helps, why not give me the strongest treatment available?”
The MOSAIC trial showed that adding oxaliplatin to fluorouracil significantly improved outcomes for patients with stage III colon cancer.
However, the additional benefit of oxaliplatin has not been clearly demonstrated for the average patient with stage II disease.
Current ASCO guidance therefore does not recommend routinely adding oxaliplatin for every patient with stage II colon cancer.
Oxaliplatin can also cause numbness, tingling or pain in the hands and feet. This is called peripheral neuropathy.
Neuropathy may improve after treatment, but it can sometimes remain for months, and in a smaller number of patients it may be permanent.
For selected patients with higher-risk stage II disease, oxaliplatin may still be discussed. However, the possible benefit must be carefully balanced against the risk of toxicity.
Is tablet chemotherapy really effective?
Yes.
Capecitabine is an oral fluoropyrimidine chemotherapy. The body converts it into 5-FU.
The X-ACT trial compared capecitabine tablets with an older intravenous 5-FU and leucovorin chemotherapy regimen after colon cancer surgery.
Capecitabine was shown to be an effective alternative to intravenous fluorouracil.
That trial involved patients with stage III colon cancer. Therefore, it does not prove that every patient with stage II disease needs capecitabine.
However, it clearly demonstrates an important point:
Taking chemotherapy as tablets does not automatically make it less effective than chemotherapy given through a drip.
When chemotherapy is appropriate for stage II colon cancer, capecitabine alone may be considered for some patients.
The decision depends on:
- The pathological risk features
- MMR or MSI status
- Kidney function
- General health
- Other medicines
- The patient’s ability to take tablets safely and consistently
- The patient’s preferences
How do we make chemotherapy safer?
One concern many patients have is the possibility of severe side effects.
Capecitabine and 5-FU are broken down by an enzyme called dihydropyrimidine dehydrogenase, or DPD.
The instructions for producing this enzyme are contained in a gene called DPYD.
Some people carry changes in the DPYD gene that reduce the activity of the DPD enzyme. This can cause fluoropyrimidine chemotherapy to build up in the body and lead to severe or potentially life-threatening side effects.
DPYD genotyping can identify several important gene variants associated with reduced DPD activity.
If a clinically significant variant is found, the treating oncologist may:
- Begin treatment at a lower dose
- Adjust the treatment plan
- Consider an alternative treatment
In Australia, DPYD genotyping was added to the Medicare Benefits Schedule on November 1, 2025.
It is more accurate to describe the test as Medicare-listed or Medicare-rebatable rather than saying that it will always be completely free, because eligibility and possible out-of-pocket costs may vary.
DPYD testing can help make treatment safer by identifying some patients who may require a lower dose or a different treatment.
Patients still require careful education, monitoring and rapid assessment if significant symptoms develop.
What this means for you
Suppose your pathology shows:
- T3 colon cancer
- 16 lymph nodes examined
- No cancer in the lymph nodes
- Clear surgical margins
- No bowel obstruction or perforation
- No lymphovascular or perineural invasion
- No other high-risk pathological features
In this situation, surgery alone may be sufficient, and many patients remain cancer-free without chemotherapy.
So, chemotherapy is not routinely recommended for every patient.
My role may be to explain why the expected additional benefit is small and why avoiding chemotherapy may be entirely reasonable.
However, the MMR or MSI result must also be reviewed.
If the tumour is dMMR or MSI-high, fluoropyrimidine chemotherapy alone is generally not routinely recommended.
If high-risk features are present—particularly T4 disease—the balance may shift towards chemotherapy.
The final decision should always be individualised.
Key takeaways
- Many patients with lower-risk T3N0 colon cancer do not routinely need chemotherapy after surgery.
The decision depends on the complete pathology report, the number of lymph nodes examined and the tumour’s MMR or MSI result.
- The average benefit of chemotherapy in stage II disease is usually small.
The QUASAR trial estimated an improvement in five-year survival of approximately three to four percentage points, although the benefit may be higher or lower for an individual patient.
- Tablet chemotherapy is not automatically weaker than chemotherapy given through a drip.
When chemotherapy is appropriate, capecitabine may be considered for selected patients, while oxaliplatin is not routinely required for every patient with stage II disease.
- Treatment should be personalised and made as safe as possible.
MMR/MSI testing helps guide whether chemotherapy is likely to be useful, while DPYD testing can identify some patients at increased risk of severe side effects from capecitabine or 5-FU.
Key evidence
- QUASAR Collaborative Group. Adjuvant chemotherapy versus observation in patients with colorectal cancer: a randomised study. Lancet. 2007;370(9604):2020-2029. doi:10.1016/S0140-6736(07)61866-2
- Bray A, Chang GJ, Ciombor KK, et al. NCCN Clinical Practice Guidelines in Oncology: Colon Cancer. Version 2.2026. National Comprehensive Cancer Network; 2026. https://www.nccn.org/guidelines/guidelines-detail?category=1&id=1428
- Baxter NN, Kennedy EB, Bergsland E, et al. Adjuvant therapy for stage II colon cancer: ASCO guideline update. J Clin Oncol. 2022;40(8):892-910. doi:10.1200/JCO.21.02538
- André T, Boni C, Mounedji-Boudiaf L, et al. Oxaliplatin, fluorouracil, and leucovorin as adjuvant treatment for colon cancer. N Engl J Med. 2004;350(23):2343-2351. doi:10.1056/NEJMoa032709
- André T, de Gramont A, Vernerey D, et al. Adjuvant fluorouracil, leucovorin, and oxaliplatin in stage II to III colon cancer: updated 10-year survival and outcomes according to BRAF mutation and mismatch repair status of the MOSAIC study. J Clin Oncol. 2015;33(35):4176-4187. doi:10.1200/JCO.2015.63.4238
- Twelves C, Wong A, Nowacki MP, et al. Capecitabine as adjuvant treatment for stage III colon cancer. N Engl J Med. 2005;352(26):2696-2704. doi:10.1056/NEJMoa043116
- eviQ. Dihydropyrimidine dehydrogenase (DPD) enzyme deficiency. Cancer Institute NSW. Accessed July 22, 2026. https://www.eviq.org.au/clinical-resources/side-effect-and-toxicity-management/prophylaxis-and-treatment/1744-dihydropyrimidine-dehydrogenase-dpd-enzyme
Frequently asked questions (FAQs)
If my surgeon removed all the cancer, why do I need to see an oncologist?
The operation may have removed all visible cancer.
The oncologist reviews whether there is a meaningful risk that microscopic cancer cells could remain elsewhere in the body and whether chemotherapy would reduce that risk enough to justify treatment.
The consultation may result in a recommendation for observation rather than chemotherapy.
Does T3 mean the cancer had spread outside the bowel?
T3 means the cancer had grown through the muscle layer of the bowel into the surrounding tissue.
It does not automatically mean that it had spread to the lymph nodes or distant organs.
If all lymph nodes were negative and there was no distant spread, it is classified as stage II rather than stage III or IV.
Is tablet chemotherapy weaker than chemotherapy given through a drip?
No.
Capecitabine is converted into 5-FU inside the body and is an established chemotherapy treatment.
The route of administration does not by itself determine how effective a treatment is.
Why don’t all patients with stage II colon cancer receive oxaliplatin?
The added benefit of oxaliplatin is uncertain for many patients with stage II disease.
It can also cause long-lasting nerve damage.
For this reason, it is generally reserved for carefully selected patients whose risk may justify the additional toxicity.
What is MMR or MSI testing?
MMR and MSI tests assess the tumour’s DNA repair system.
The results provide information about prognosis and chemotherapy decisions. In some patients, an abnormal result may also lead to further assessment for an inherited cancer condition such as Lynch syndrome.
What is DPYD testing, and does a normal result mean I will not have side effects?
DPYD testing looks for genetic changes that can increase the risk of severe side effects from capecitabine or 5-FU. If a significant change is found, the dose or treatment may be adjusted.
A normal result does not guarantee that side effects will not occur, so patients still need careful monitoring.
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)