An Immunotherapy Could Help Some Rectal Cancer Patients Avoid Surgery, Radiation and Chemotherapy

A cancer treatment result that could change more than survival

For many people with locally advanced rectal cancer, beating the disease can require chemotherapy, radiation and major surgery. Those treatments save lives, but they can also leave permanent consequences, including a colostomy, infertility, and changes to bowel, urinary or sexual function.

A new Phase II trial suggests that a carefully selected group of patients may be able to take a very different path: six months of immunotherapy alone, followed by close monitoring if the tumor can no longer be detected.

What did the trial find?

The global AZUR-1 study enrolled 154 people with untreated stage II or III rectal cancer carrying one of two related biomarkers: mismatch-repair deficiency (dMMR) or high microsatellite instability (MSI-H). Participants received nine infusions of the immunotherapy drug dostarlimab, also sold as Jemperli, once every three weeks.

GSK announced that the study met its main goal: a clinically meaningful share of participants had a “clinical complete response” that lasted at least 12 months. In everyday language, doctors could find no sign of the tumor using the examinations and scans specified by the trial.

That is not the same as proving every cancer cell has been eliminated forever. It does mean that some patients may be able to delay—or potentially avoid—chemotherapy, radiation and surgery while remaining under intensive surveillance.

Why can immunotherapy work so well in this group?

dMMR/MSI-H tumors have faulty machinery for repairing damaged DNA. As genetic errors accumulate, the cancer cells tend to look more unusual to the immune system. Dostarlimab blocks PD-1, a molecular “brake” that tumors can exploit to suppress immune attack. Releasing that brake can help T cells recognize and attack the cancer.

The biology is powerful but narrowly applicable. Only about 5% to 10% of rectal cancers carry these biomarkers, so tumor testing is essential. The result should not be interpreted as a universal cure for rectal cancer or cancer generally.

Why doctors are paying attention

The larger international trial builds on a striking study led by Memorial Sloan Kettering Cancer Center. In that earlier work, every one of the initial 12 patients achieved a clinical complete response after dostarlimab. Longer follow-up and expanded cohorts strengthened the case that the observation was not simply a tiny-study accident.

AZUR-1 matters because it tests the approach across more patients and treatment centers. If regulators accept the evidence, dostarlimab could become the first approved immunotherapy intended to let some people with this molecular subtype avoid the standard combination of chemotherapy, radiation and surgery.

The missing numbers matter

The announcement is encouraging, but it is not yet a complete scientific report. GSK has not disclosed the exact 12-month response rate, detailed side-effect figures, recurrence data or subgroup results. Those findings are expected at a future medical meeting.

The study is also open-label and single-arm: everyone received dostarlimab, with no randomized control group receiving standard treatment. Comparisons therefore rely partly on historical results. Longer follow-up is crucial because a tumor that is invisible today can regrow later, and “watch-and-wait” care requires repeated scans, endoscopy and clinical examinations.

Immune checkpoint drugs can also cause the immune system to attack healthy organs, producing problems such as inflammation of the lungs, bowel, liver, kidneys or hormone-producing glands. Dostarlimab is not currently approved anywhere specifically for rectal cancer.

What happens next?

GSK plans to submit the interim findings to regulators, including for an accelerated review in the United States. Until detailed results are published and authorities complete their assessment, this remains a promising investigational strategy—not a replacement patients should seek outside specialist oncology care.

The breakthrough is therefore both exciting and precise: it may not help most people with rectal cancer, but for the biomarker-defined minority who qualify, treatment could become dramatically less destructive without giving up the goal of controlling the disease.