FDA Approves Immunotherapy Plus Chemotherapy for Stage III Colon Cancer: What Patients Need to Know
Quick Answers
• What happened? The U.S. Food and Drug Administration (FDA) approved atezolizumab, also called Tecentriq, to be used with chemotherapy after surgery for stage III colon cancer with deficient mismatch repair, or dMMR.
• Who is it for? People whose colon cancer was removed by surgery, had spread to nearby lymph nodes (stage III), and whose tumor tests show dMMR.
• How well did it work? In the phase 3 ATOMIC trial with 712 patients, 86.3% of people who got immunotherapy plus chemotherapy were alive and free of cancer at 3 years, compared with 76.2% with chemotherapy alone.
• Why does it matter? It is the first FDA-approved immunotherapy treatment used after surgery for this type of colon cancer, and it cut the risk of recurrence or death by half.
What Happened This Week in Colon Cancer News?
On October 8, 2026, the FDA approved atezolizumab (Tecentriq, made by Genentech) in combination with chemotherapy for the adjuvant treatment of stage III mismatch repair deficient (dMMR) colon cancer.
Adjuvant treatment means treatment given after surgery. The goal is to kill any tiny cancer cells that may be left behind. Those cells are too small to see, but they can cause the cancer to come back.
The FDA also approved an under-the-skin form, atezolizumab and hyaluronidase-tqjs (Tecentriq Hybreza), with the same chemotherapy for patients age 12 and older who weigh at least 40 kg (about 88 pounds). The intravenous (IV) form is approved for adults and children age 2 and older.
News and expert coverage of the approval continued all week, including a summary in Cancer Today magazine's "Week in Cancer News" on October 15, 2026.
What Is dMMR Colon Cancer?
MMR stands for mismatch repair. Your cells have a repair system that fixes small mistakes when DNA is copied.
Think of it like spell-check for your DNA.
When that spell-check system does not work, it is called deficient mismatch repair, or dMMR. Mistakes build up in the DNA. That can help cancer grow. But it can also make the cancer easier for the immune system to spot.
About 15% of colorectal cancers are dMMR. A lab test on the tumor can show if a cancer is dMMR. This is why tumor testing matters. The test result can change which treatments are offered after surgery.
Tumor biology can affect treatment in other ways too — see our post: Can Bacteria Inside a Tumor Affect How Well Chemotherapy Works?
What Did the ATOMIC Trial Find?
The approval is based on the phase 3 ATOMIC trial (NCT02912559), led by researchers at Mayo Clinic. The study enrolled 712 people with stage III dMMR colon cancer. All of them had surgery to remove the primary tumor.
People in the study were split into two groups:
1. Immunotherapy plus chemotherapy: Atezolizumab plus mFOLFOX6 chemotherapy for 12 cycles, followed by atezolizumab alone for 6 more months.
2. Chemotherapy alone: mFOLFOX6 for 12 cycles.
mFOLFOX6 is a common chemotherapy plan. It uses fluorouracil (5-FU), leucovorin, and oxaliplatin.
The key results
• At 3 years, 86.3% of people in the immunotherapy plus chemotherapy group were alive and free of disease.
• At 3 years, 76.2% of people in the chemotherapy-only group were alive and free of disease.
• That is a 50% lower risk of the cancer coming back or death (hazard ratio 0.50).
• The median disease-free survival was not reached in either group, which means more than half of the people in each group were still free of disease at the time of the analysis.
Lead investigator Dr. Frank Sinicrope of Mayo Clinic called the regimen practice-changing for this group of patients, noting it is the first study to show a benefit from immunotherapy after surgery for locally advanced dMMR colon cancer.
So far, this treatment has been shown to help keep cancer from coming back. It has not yet been shown to help people live longer overall — at 5 years, survival was similar in both groups (89.7% with atezolizumab plus chemotherapy vs. 87.9% with chemotherapy alone).
How Is Atezolizumab Plus Chemotherapy Given?
Atezolizumab is an immune checkpoint inhibitor. It blocks a protein called PD-L1. That helps the immune system find and attack cancer cells.
In the ATOMIC plan:
• Chemotherapy and atezolizumab are given together for about 6 months (12 cycles of mFOLFOX6).
• Then atezolizumab is given alone for 6 more months.
• Treatment may stop sooner if the cancer comes back or if side effects become too hard to tolerate.
Your oncologist will confirm if this plan is right for you. It is only approved for colon cancer that tests as dMMR, not for all colon cancers.
What Side Effects Should Patients Watch For?
Both chemotherapy and immunotherapy can cause side effects. It is important to tell your care team early if you feel worse.
Common chemotherapy side effects with FOLFOX can include:
• Diarrhea and nausea
• Mouth sores
• Tiredness (fatigue)
• Low blood counts
• Numbness or tingling in the hands and feet from oxaliplatin
• Dehydration and loss of electrolytes when diarrhea or vomiting is severe
Nerve symptoms can start even before chemotherapy in some colorectal cancers. Read more in our post: Colorectal Cancer May Cause Peripheral Neuropathy Before Chemotherapy
Immunotherapy side effects can be different. Because atezolizumab affects the immune system, it can cause immune-related side effects in the lungs, gut, liver, skin, or hormone glands. The FDA prescribing information also warns about infusion reactions and risks around stem-cell transplant and pregnancy.
Call your care team right away for new or worse cough, severe diarrhea, yellow skin, a severe rash, extreme tiredness, or signs of dehydration such as dizziness, very low urine output, muscle cramps, or a racing heart.
Why Supportive Care Matters During FOLFOX Chemotherapy
Cancer treatment is not only about fighting the tumor. Staying strong enough to stay on treatment matters too.
Learn more in our post: Cancer Treatment Is More Than Fighting the Tumor: Why Supportive Care Matters
Diarrhea, mouth sores, and poor intake can quickly lead to dehydration and electrolyte loss. Platinum-based and fluorouracil-based chemotherapy can also harm the lining of the gut. When the gut lining is hurt, it is harder to absorb fluids and nutrients.
That is the supportive-care space HuMOLYTE was made for. HuMOLYTE is a medical food for use under medical supervision. It is designed to support hydration and electrolyte balance — including magnesium, which many standard drinks do not replace — and gut health during chemotherapy, with 2'-fucosyllactose (2'-FL), a human milk oligosaccharide (HMO). See the research in our post: 2′-FL & Chemotherapy-Induced Mucositis: HuMOLYTE Study
HuMOLYTE does not treat cancer, and it does not replace chemotherapy, immunotherapy, or care from your oncology team. Talk with your oncologist before starting any new product during treatment, including HuMOLYTE.
Practical steps that often help patients during chemotherapy include:
• Track fluid intake, bathroom trips, weight, and energy each day.
• Report diarrhea, mouth sores, or cramps early — do not wait for the next visit.
• Ask if you need lab checks for electrolytes, including magnesium and potassium.
• Ask for a dietitian referral if eating becomes hard.
Questions to Ask Your Oncologist
1. Was my tumor tested for mismatch repair? Is it dMMR?
2. Am I a candidate for atezolizumab plus chemotherapy after surgery?
3. What are the benefits and risks for me, based on my age and other health issues?
4. How will we watch for immune-related side effects?
5. What is our plan for diarrhea, dehydration, and electrolyte loss during FOLFOX?
6. Who should I call after hours if side effects get severe?
The Bottom Line
The FDA approval of atezolizumab plus chemotherapy on October 8, 2026, is a major step for people with stage III dMMR colon cancer. In the ATOMIC trial, adding immunotherapy to chemotherapy after surgery raised 3-year disease-free survival from 76.2% to 86.3% and cut the risk of recurrence or death by 50%.
If you or a loved one has stage III colon cancer, ask if the tumor was tested for dMMR. That one test can open the door to this new option — and a clear plan for supportive care can help you stay hydrated, nourished, and on track during treatment.
Frequently Asked Questions
What is the new FDA approval for colon cancer in October 2026?
The FDA approved atezolizumab (Tecentriq) plus a fluoropyrimidine and oxaliplatin chemotherapy (such as mFOLFOX6) after surgery for stage III mismatch repair deficient (dMMR) colon cancer.
Who can get atezolizumab plus chemotherapy for colon cancer?
Adults and children age 2 and older with stage III dMMR colon cancer that has been removed by surgery. The under-the-skin form, Tecentriq Hybreza, is approved for patients age 12 and older who weigh at least 40 kg.
How much did atezolizumab help in the ATOMIC trial?
At 3 years, 86.3% of patients who got atezolizumab plus chemotherapy were alive and free of disease, compared with 76.2% with chemotherapy alone. That equals a 50% lower risk of recurrence or death (hazard ratio 0.50).
Does this approval apply to all colon cancers?
No. It applies only to stage III colon cancer that tests as mismatch repair deficient (dMMR). That is about 15% of colorectal cancers.
What are the main side effects to watch for?
Chemotherapy can cause diarrhea, nausea, mouth sores, fatigue, and numbness in the hands and feet. Immunotherapy can cause immune-related side effects in organs such as the lungs, gut, and liver. Report severe or new symptoms to your care team right away.
Sources
• Cancer Today — The Week in Cancer News: Immunotherapy for Colon Cancer
For more information on how HuMOLYTE can support your gut health during chemotherapy, visit our product page or consult your health care provider.
This blog was reviewed by Dr. Sourabh Kharait.
This blog is for educational purposes only and is not intended as medical advice. Always consult with your healthcare provider before making any changes to your treatment plan, hydration strategies, or diet. The information provided here is based on general insights and may not apply to individual circumstances.
