FDA approves Tecentriq for some people with stage III colon cancer

The U.S. Food and Drug Administration (FDA) has approved the immunotherapy drug Tecentriq (atezolizumab) for some people with stage III colon cancer. It is now approved to be given with standard chemotherapy after surgery, for people whose tumors have a feature called deficient mismatch repair, or dMMR.

Genentech announced the approval on October 8, 2026. It is the first immunotherapy approved for this use, adding a new option for a group of patients who face a high risk of their cancer coming back.

Why this matters

Nearly a quarter of colon cancers are found at stage III, when the cancer has reached nearby lymph nodes but not distant organs. Treatment usually means surgery to remove the tumor, followed by chemotherapy (called adjuvant therapy) to lower the chance of the cancer returning.

Even with that treatment, nearly 30% of people with stage III colon cancer have a recurrence within five years. And until now, post-surgery treatment has been the same whether or not a tumor was dMMR. This approval is the first to tailor it to that tumor biology.

What the study found

The approval is based on the Phase III ATOMIC trial, sponsored by the National Cancer Institute and published in The New England Journal of Medicine. It enrolled 712 people with stage III dMMR colon cancer who had already had surgery.

Half received standard chemotherapy (a regimen called mFOLFOX6) for six months. The other half received the same chemotherapy plus Tecentriq for six months, then Tecentriq alone for six more months.

•         Adding Tecentriq cut the risk of the cancer coming back, or of death, by 50% compared with chemotherapy alone.

•         At three years, 86% of people in the Tecentriq group were living without their cancer returning, compared with 76% in the chemotherapy-only group.

Dr. Frank Sinicrope of the Mayo Clinic, who led the trial, called the combination “a practice-changing regimen.”

Who this approval is for

Mismatch repair proteins work like a cell's spell-checker, fixing small errors when DNA is copied. When they are deficient or don't work properly, mistakes pile up inside the tumor. That makes the cancer easier for the immune system to spot, which is why immunotherapy can help.

About 15% of people with colon cancer have dMMR tumors (or a closely related feature called microsatellite instability, or MSI-high). The approval applies specifically to stage III colon cancer that a lab test has shown to be dMMR. It does not cover rectal cancer.

Guidelines recommend testing every colorectal cancer tumor for mismatch repair or MSI status. The approval covers two versions of the drug: Tecentriq, given by IV, and Tecentriq Hybreza, given as an injection under the skin.

What to know about side effects

Because Tecentriq works through the immune system, it can sometimes cause the immune system to attack healthy organs, such as the lungs, intestines, liver, hormone glands, kidneys, or skin. These problems can be serious and can appear during or after treatment, so any new or worsening symptom should be reported to the care team right away.

When given with chemotherapy for colon cancer, the most common side effects included tiredness, nausea, numbness or tingling in the hands and feet, constipation, diarrhea, belly pain, low appetite, mouth sores, and changes in taste. People with autoimmune conditions such as Crohn's disease, ulcerative colitis, or lupus should share that history before starting treatment.

Questions to bring to your care team

For anyone diagnosed with stage III colon cancer, these questions can help guide the conversation about treatment after surgery:

•         Has my tumor been tested for mismatch repair (MMR) or MSI status, and what were the results?

•         If my tumor is dMMR, could adding Tecentriq to my chemotherapy be an option for me?

•         How would it change the length of my treatment and how often I come in?

•         Which side effects should I watch for, and who should I call if they happen?

The Alliance is here for you

Every new treatment option is built on the people who volunteer for clinical trials. We're grateful to the patients, families, and care teams who took part in ATOMIC.

If you have questions about this news or what it could mean for your treatment, the Colorectal Cancer Alliance’s cancer care team is available to help at our free Helpline: (877) 422-2030.