Editorial Note: This article is an internal production sample used exclusively for contributor outreach. All content, author bios, and associated data are strictly illustrative and fictional.
For most people with locally advanced rectal cancer, standard treatment is demanding. It typically combines chemotherapy, radiation, and surgery, and it can leave patients with lasting problems with bowel control, bladder function, sexual health, and fertility. Some need a permanent colostomy.
That is why results for a drug called dostarlimab have drawn so much attention from oncologists. For a specific subgroup of patients, it may offer a path that avoids surgery and radiation entirely. The FDA has now agreed to review it for this use on an expedited basis.
What the Research Found
The key evidence comes from a phase 2 study at Memorial Sloan Kettering Cancer Center published in the New England Journal of Medicine in 2025. Researchers treated patients with early-stage tumors that were "mismatch repair-deficient" (explained below) with six months of dostarlimab, an immunotherapy drug that blocks a protein called PD-1. Patients whose tumors disappeared could choose to skip surgery and be monitored closely instead.
The study included 117 patients. In the rectal cancer group, all 49 patients who completed treatment had a clinical complete response, meaning doctors could find no remaining tumor on exams, scans, and endoscopy, and all chose to avoid surgery. Thirty-seven had a sustained complete response at 12 months, which met the study's efficacy goal.
Results in other cancer types were promising but less uniform. Among 54 patients with non-rectal tumors, 35 had a complete response. Across the whole study, recurrence-free survival at two years was 92%, with a median follow-up of 20 months. Most patients (95%) had either no side effects or mild, reversible ones.
A larger, international trial is now confirming these findings. The AZUR-1 trial enrolled 154 patients who received dostarlimab every three weeks for nine cycles over six months. In July 2026, drugmaker GSK announced that the trial met its primary goal at an interim analysis, showing a meaningful rate of sustained complete responses at 12 months with no new safety concerns. The FDA has since accepted the application for priority review, with a decision expected by February 2027. Full results are expected at a scientific meeting later in 2026.
Why Only Some Patients Benefit
This is the most important point for readers to understand. These results apply only to tumors that are mismatch repair-deficient (dMMR), also called microsatellite instability-high (MSI-H).
Mismatch repair is the cell's spell-check system for DNA. When it is broken, tumors pile up hundreds or thousands of mutations. Those mutations make cancer cells look foreign to the immune system, which is why drugs that release the immune system's brakes work so well against them.
Only about 5% to 10% of rectal cancers are dMMR or MSI-H. For the other 90% or more, this approach is not expected to work, and standard treatment remains the right path.
Why These Findings Matter in Cancer Care
Even before FDA action, the field has shifted. Immune checkpoint drugs including dostarlimab are already recommended by the National Comprehensive Cancer Network as standard first-line treatment for dMMR locally advanced rectal cancer, although the drug is not yet approved for this use. Dostarlimab is currently FDA-approved for certain dMMR endometrial cancers and for advanced dMMR solid tumors without other good options.
The implications are especially meaningful as rectal cancer rises among younger adults. For a 38-year-old, avoiding radiation and major pelvic surgery can mean preserving fertility, sexual function and normal bowel control for decades.
What the Research Does, and Does Not, Show
The results are striking, but oncologists will want several questions answered before treating this as settled.
The studies are single-arm. Neither study randomly compared dostarlimab with standard treatment. Because standard chemotherapy, radiation and surgery rarely make these tumors fully disappear on their own, a single-arm design is reasonable here, but it limits direct comparisons.
Follow-up is still relatively short. Two-year results are encouraging. However, the goal of treating early-stage cancer is a cure, and rectal cancer can recur years later.
"Clinical complete response" is not the same as proof of cure. It means doctors cannot detect cancer with current tools. Patients who skip surgery need intensive surveillance with regular scans and endoscopies, often for years, and must commit to that schedule.
AZUR-1 data are not yet public in detail. Until full results are presented and published, the exact response rate in a larger, international population is unknown.
What Oncologists Want Patients To Know
If you or a family member is diagnosed with colorectal cancer, ask whether the tumor has been tested for mismatch repair status. The answer can change the entire treatment plan. Patients who are dMMR should ask whether they are candidates for immunotherapy first, ideally at a center with experience in this approach.
Patients whose tumors are not dMMR should not feel they are receiving second-rate care. Standard treatment remains highly effective for many people, and researchers are actively studying ways to extend organ-preserving strategies to more patients.
What Could Happen Next
The FDA's decision, expected by February 2027, could make dostarlimab the first immunotherapy approved specifically as initial treatment for dMMR rectal cancer. Researchers will also be watching longer-term recurrence data and whether similar results hold for dMMR cancers in other organs, where responses have been less consistent.
The Bottom Line
For the small group of patients with mismatch repair-deficient rectal cancer, immunotherapy alone may make it possible to avoid surgery, radiation and chemotherapy. The evidence so far is remarkable but still maturing. For everyone with colorectal cancer, the most useful takeaway is simple: make sure the tumor has been tested.
About the Author
Morgan Demo, MD, is a board-certified medical oncologist at Fictional Valley Medical Center in Exampleton, ST, where she specializes in colorectal and other gastrointestinal cancers, including immunotherapy and organ-preserving treatment for rectal cancer. She completed her hematology and oncology fellowship at Example University Medical Center and is an Assistant Professor of Medicine at Fictional Valley University. Her work focuses on immunotherapy clinical trials and nonoperative management of rectal cancer.
Contact: Department of Hematology and Oncology, Fictional Valley Medical Center, 300 Specimen Road, Exampleton, ST 00003 | [email protected] | (555) 010-0303
Disclosures: Dr. Demo reports no financial relationships with GSK or other makers of immune checkpoint inhibitors and was not an investigator on the AZUR-1 trial.
Author's Sources
- Cercek A, et al. "Nonoperative Management of Mismatch Repair–Deficient Tumors." New England Journal of Medicine, 2025;392(23):2297–2308. Abstract via MSK.
- GSK. "Jemperli (dostarlimab) achieves sustained clinical complete responses in dMMR/MSI-H locally advanced rectal cancer." July 13, 2026.
- CancerNetwork. "FDA Accepts Priority Review for Dostarlimab in dMMR/MSI-H Rectal Cancer." 2026.
- Cancer Therapy Advisor. "FDA Priority Review Granted to Dostarlimab for Rectal Cancer." 2026.
- PCORI Health Care Horizon Scanning. "Dostarlimab (Jemperli) to treat locally advanced rectal cancer."
- ClinicalTrials.gov. AZUR-1 (NCT05723562).
Published by Medicaldaily.com
