For a Small Group of Rectal Cancer Patients, the FDA Just Made Surgery Optional.

The standard treatment for locally advanced rectal cancer is one of the most punishing sequences in oncology: weeks of chemotherapy and radiation to shrink the tumor, then surgery to remove the rectum — an operation that can leave patients with permanent changes to bowel, urinary and sexual function, and in some cases a colostomy for life. On October 19, 2026, the FDA approved a use of the immunotherapy dostarlimab (Jemperli) that may let a defined group of these patients skip all three.

The approval covers adults with previously untreated stage II or stage III locally advanced rectal cancer whose tumors are mismatch repair deficient (dMMR) or microsatellite instability-high (MSI-H), confirmed by an FDA-authorized test. Published estimates suggest that is roughly 3% of locally advanced rectal cancers — a small slice of a common disease, but for the people in it, a different life.

Why this tumor type responds so dramatically

Mismatch repair is the cell’s spell-checker for DNA copying. Tumors that lack it accumulate enormous numbers of mutations, and mutated proteins make unusually visible targets for the immune system. Dostarlimab is a PD-1 blocker — it removes a molecular brake on T-cells — and in dMMR tumors the unbraked immune system often does the rest. This is the same biology behind the striking Memorial Sloan Kettering pilot results that first drew attention to this approach: in a small, closely watched cohort, every patient who completed dostarlimab alone had a complete clinical response, with no chemo, radiation or surgery.

The FDA’s decision rests on that line of evidence, and the agency moved fast — it said the review was completed nearly four months ahead of schedule. The acting commissioner framed it as a commitment to closing the gap between scientific progress and patient access.

For the roughly 3% of rectal cancer patients whose tumors are mismatch repair deficient, the conversation with the surgeon just changed. For the other 97%, nothing about this approval applies — yet.

What “accelerated approval” actually means here

This is an accelerated approval, not a full one. The FDA accepted an intermediate endpoint — complete clinical response, meaning no detectable tumor — as reasonably likely to predict lasting benefit, and the manufacturer must confirm that benefit in continued study. The open questions are real: how durable the responses are at five and ten years, how often the cancer returns after a watch-and-wait approach, and whether skipping surgery trades one set of risks for a longer, less certain surveillance burden of scopes, scans and MRIs.

There is also a testing gap. The approval only helps patients whose tumors are tested for mismatch repair status — and testing is not yet universal in every community hospital where rectal cancer is first diagnosed. A patient whose tumor is never tested cannot benefit from a drug approved for a biomarker nobody looked for.

The bigger pattern

The same week’s oncology news pointed in the same direction. Earlier in October the FDA approved atezolizumab with chemotherapy as adjuvant treatment for stage III dMMR colon cancer, based on the ATOMIC trial — another case of immunotherapy performing outsized work in mismatch-repair-deficient disease. The through-line is that “dMMR” is becoming less a footnote in a pathology report and more the first question asked, because it increasingly decides the entire treatment path.

What a reader should take from this: if you or someone you love is diagnosed with locally advanced rectal cancer, the actionable sentence is “has my tumor been tested for mismatch repair deficiency?” If the answer is yes and the result is dMMR, this approval is worth a real conversation with an oncologist. If the tumor is not dMMR, the standard sequence remains the evidence-based path — and the trials now running will determine whether that changes too.

This article is general information, not medical advice. See our Editorial Standards.