FDA approves immunotherapy for MSI-H/dMMR stage II & III rectal cancer

On October 19, 2026, the U.S. Food and Drug Administration (FDA) approved dostarlimab (brand name Jemperli) as the first and only immunotherapy for adults with stage II or III rectal cancer that has a biomarker called MSI-H or dMMR. In a clinical trial, many patients who received dostarlimab alone had no detectable cancer a year or more later, without chemotherapy, radiation, or surgery.

“People facing rectal cancer are often thinking not only about treating their disease, but also worrying about what life will look like afterwards,” said Michael Sapienza, CEO of the Colorectal Cancer Alliance. “The possibility of avoiding chemotherapy, radiation and surgery represents a meaningful advance for patients and their families.”

Who this approval is for

The approval covers adults whose rectal cancer is both:

●     Stage II or III. Doctors call this “locally advanced.” The cancer has grown through the muscle layer of the rectal wall, or reached nearby lymph nodes, but has not spread to distant organs.

●      MSI-H or dMMR. These stand for microsatellite instability-high and mismatch repair deficient. About 5 to 10 out of every 100 rectal cancers are MSI-H/dMMR.

How dostarlimab works

Healthy cells have a built-in “spell-check” that fixes mistakes when DNA is copied. In MSI-H/dMMR tumors, that system is broken, so mistakes pile up and the cancer becomes easier for the immune system to spot. Dostarlimab blocks PD-1, a “brake” on immune cells that cancer cells press to hide, so your immune system can attack the cancer.

What the research showed

The approval is based on AZUR-1, a phase II trial in which 154 people with previously untreated stage II or III MSI-H/dMMR rectal cancer received dostarlimab alone. There were nine IV treatments over about six months. The trial did not compare it with standard treatment.

Researchers looked for a “clinical complete response,” which means no sign of cancer on exams, scans, or scopes for at least 12 months. Among patients whose results could be measured:

●     About 2 in 3 (68%) had a complete response lasting at least a year, without surgery, based on their own doctors’ assessments.

●     About 3 in 4 (76%) had no evidence of cancer a year or more after treatment. This exploratory analysis adds 12 patients whose tissue showed no remaining cancer after surgery.

●     No one who responded has seen their cancer come back so far. Half of patients have been followed for more than two years.

●      On the trial’s main measure, independent reviewers have confirmed a 12-month complete response in 47%. Another 38 patients have had a complete response but haven’t reached the one-year mark yet, so this number is still being updated.

Not everyone responded completely. The trial is ongoing, and more detailed results from this interim analysis will be presented at the European Society for Medical Oncology Congress.

Side effects and accelerated approval

Standard treatment can cause lasting bowel, bladder, and sexual problems, affect fertility, and raise the risk of a second cancer. For patients who respond to dostarlimab, avoiding it may help protect their quality of life.

Dostarlimab has its own side effects. The most common in the trial were tiredness (32%), rash (22%), diarrhea (18%), and itching (17%). Serious side effects happened in 20% of patients, and 3% stopped treatment because of them. Immunotherapy can sometimes cause inflammation in healthy organs, so tell your care team right away about any new or worsening symptoms.

The FDA granted accelerated approval, which helps promising treatments for serious diseases reach patients sooner based on early results. Continued approval may depend on what further studies show.

Why biomarker testing matters

Biomarker testing, usually done on biopsy tissue, is the only way to know whether a tumor is MSI-H/dMMR. Most rectal cancers are not, and for those patients, chemotherapy, radiation, and surgery remain the standard approach.

“Biomarker testing at diagnosis will be essential to identifying patients who may be eligible for this treatment and helping them understand their options,” Sapienza said.

An MSI-H/dMMR result can sometimes point to Lynch syndrome, an inherited condition that raises the risk of colorectal and other cancers. If your tumor tests positive, ask whether genetic counseling makes sense for you and your family.

Questions to ask your care team

●     Has my tumor been tested for MSI or MMR, and what were the results?

●     If my tumor is MSI-H/dMMR, is dostarlimab an option, and how would it differ from standard care?

●      If my cancer responds, how often will I need checkups, scans, and scopes?

We’re here to help

New treatment options can be difficult to understand. Our cancer care team can answer your questions, help you prepare for conversations with your doctor, and connect you with resources. Call the Colorectal Cancer Alliance Helpline at (877) 422-2030.

Learn more about biomarker testing and what your results can mean for your treatment.