FDA Approves Dostarlimab for dMMR Rectal Cancer, an Option That May Spare Some Patients Surgery
The first immunotherapy cleared for locally advanced rectal cancer with a specific tumour fingerprint, approved four months early on interim data that still needs confirming.
Monday, October 19, 2026/2 min read
For most people with locally advanced rectal cancer, treatment means some combination of chemotherapy, radiation and surgery. On 19 October the US Food and Drug Administration approved a drug that may let a small group of patients avoid all three. The agency granted accelerated approval to dostarlimab (Jemperli) for adults with stage II or III rectal cancer whose tumours are mismatch repair deficient (dMMR) or microsatellite instability high (MSI-H), according to the FDA's announcement.
The FDA estimates that about 3 percent of locally advanced rectal cancers fit that profile, and a test authorised by the agency is needed to identify them. Drugmaker GSK describes Jemperli as the first and only approved immunotherapy for the group in the US.
What did the AZUR-1 trial show?
Approval rests on AZUR-1, a single-arm phase 2 trial in 154 previously untreated patients who received dostarlimab alone, 500 mg by infusion every three weeks for nine cycles, per GSK's release.
The numbers depend on who is counting. By independent central review, 47 percent of the 116 evaluable patients had a sustained clinical complete response at 12 months. Investigators rated it at 68 percent of 144 patients. After a median follow-up of more than two years, almost three-quarters had not needed surgery, radiotherapy or chemotherapy, the FDA said. The ASCO Post reported that 15 patients had surgery after dostarlimab alone because imaging suggested an incomplete response.
What are the side effects and the catch?
Dostarlimab can cause the immune system to attack healthy organs, and these reactions can be severe or fatal, the FDA said. The most common side effects, in at least 15 percent of patients, were fatigue, rash, diarrhoea and itching. GSK reported serious adverse reactions in 20 percent of patients and permanent discontinuation in 3 percent.
The catch is the evidence. No patient who reached a complete response had progressed at the data cut, the ASCO Post said, but the FDA stressed that longer follow-up is needed to know how long responses last and how often cancer comes back. It requires the sponsor to keep following patients to confirm lasting benefit. A smaller earlier study from Memorial Sloan Kettering in 50 patients is the supporting evidence, in which 93 percent were cancer-free at 12 months.
Who is this for?
Only for patients whose tumours carry the dMMR or MSI-H marker, which is why testing at diagnosis matters. Colorectal Cancer Alliance chief executive Michael Sapienza said biomarker testing will be essential to find the patients who may be eligible. Anyone else with rectal cancer is not in this group, and the approval does not change their standard options.
This article is reporting, not medical advice. Decisions about cancer treatment, testing and whether to forgo surgery or other therapy belong with an oncology team that knows the patient's history and tumour. Full AZUR-1 interim data are due at the ESMO Congress this month, and the next evidence to watch is the longer follow-up that will show whether early responses last.
Published in The Outspoken Digest
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