Dostarlimab Offers Treatment-Only Path in Rectal Cancer

A new initial pathway for a biomarker-defined group

The October 19, 2026, decision moves dostarlimab (Jemperli), a programmed death receptor-1 inhibitor, from an investigational organ-preservation strategy to an FDA-approved initial treatment option for a narrowly defined rectal cancer population. The indication covers adults with previously untreated, locally advanced stage II or III rectal cancer that is mismatch repair-deficient or microsatellite instability-high.

The practical change is substantial. Conventional management of locally advanced rectal cancer commonly combines systemic chemotherapy, pelvic radiation and surgery, although sequencing and individual components vary. Each can produce durable disease control, but pelvic surgery may require a permanent or temporary ostomy and can affect bowel, urinary and sexual function. Radiation and chemotherapy add acute and long-term toxicities.

For patients who meet the new indication, the initial discussion can instead center on immune checkpoint blockade, serial response assessment and the possibility of omitting all three conventional modalities if a complete clinical response is achieved and sustained. This is not equivalent to declaring surgery or chemoradiation unnecessary for every patient with rectal cancer. Eligibility depends on tumor biology, stage, prior treatment and the ability to complete close surveillance.

Accelerated approval also carries an important qualification. The FDA can authorize a drug based on an endpoint reasonably likely to predict clinical benefit, while requiring additional evidence to confirm that benefit. Continued approval may depend on confirmatory results.

The evidence behind organ preservation

The pivotal clinical concept came from a prospective, single-group phase 2 study of dostarlimab in previously untreated stage II or III dMMR locally advanced rectal adenocarcinoma. Participants received dostarlimab for six months. Those with a complete clinical response could enter nonoperative follow-up; chemoradiation and surgery remained planned options for patients without an adequate response.

In the initial 2022 peer-reviewed report, 12 patients had completed treatment and had at least six months of follow-up. All 12 achieved a complete clinical response. The report did not provide a comparative effect estimate, confidence interval or p-value because there was no control group. At the time of publication, none of these patients had undergone chemotherapy, radiation or surgery, and no progression or recurrence had been observed during follow-up ranging from 6 to 25 months.

A complete clinical response was determined using clinical and radiologic evaluation rather than examination of a surgically removed specimen. Assessment included endoscopy, digital rectal examination and rectal magnetic resonance imaging, with additional imaging used to look for distant disease. This distinction matters: a clinical complete response indicates that no tumor is detectable by the specified assessments, not that microscopic eradication has been proved histologically.

The early publication established proof of concept but is not a numerical substitute for the later regulatory dataset. The FDA decision and current prescribing information define the approved population and should be consulted for the agency’s full efficacy and safety analysis. The registered study also provides the protocol framework and ongoing-status information.

How initial treatment discussions change

Mismatch repair or microsatellite-instability testing now has immediate treatment-selection consequences in this setting. A patient whose tumor is confirmed as MSI-H or dMMR may be considered for dostarlimab before chemotherapy, radiation or rectal surgery, rather than receiving immunotherapy only after conventional treatment has failed.

The decision is best framed as a response-contingent pathway. Dostarlimab is the initial treatment, but omission of local and cytotoxic therapy depends on achieving and maintaining a complete clinical response. Patients with residual, recurrent or progressive disease may still need chemotherapy, radiation, surgery or another strategy selected by a multidisciplinary team.

Surveillance is therefore part of the treatment strategy, not an optional add-on. Avoiding immediate surgery means there is no resection specimen to confirm pathologic response, and a regrowth must be detected while salvage treatment remains feasible. Follow-up generally requires repeated clinical examination, endoscopy and imaging according to the protocol, label and institutional organ-preservation program.

The approval may also affect capacity and policy. Wider use will require reliable tumor testing, expert rectal MRI and endoscopy, coordinated review by medical oncology, radiation oncology, colorectal surgery, radiology and pathology, and systems that can retain patients in intensive follow-up. Access to the drug alone does not reproduce the full care model used in the study.

Safety discussions remain necessary even when chemotherapy, radiation and surgery might be avoided. The initial 12-patient publication reported no grade 3 or higher adverse events, but that sample was too small to characterize uncommon or delayed toxicities. Immune checkpoint inhibition can cause clinically important immune-mediated adverse reactions, and the current FDA prescribing information remains the appropriate source for monitoring and management requirements.

Important uncertainties remain

The central limitation is design. The supporting study was nonrandomized and initially reported results from a small, highly selected population treated by an experienced team. Without a comparator, it cannot determine whether dostarlimab improves overall survival, disease-free survival, quality of life or long-term organ function relative to modern multimodality treatment.

Follow-up is another constraint. Rectal cancer regrowth or distant recurrence may occur after an apparently complete response, so early response rates cannot establish cure. Larger numbers and longer observation are needed to define response durability, salvage-treatment success, late immune toxicities and outcomes across broader racial, geographic and practice populations.

Generalizability is intentionally narrow. The evidence does not establish the same treatment-only pathway for mismatch repair-proficient or microsatellite-stable tumors, previously treated disease, metastatic disease, or rectal cancers outside the approved stage and clinical setting. It also does not show that another PD-1 inhibitor can automatically be substituted.

The published phase 2 work reported support from GlaxoSmithKline, the manufacturer involved in dostarlimab development, along with philanthropic and federal sources; investigator disclosures accompanied the publication. Independent replication and the FDA-required confirmatory evidence will be important for determining whether the striking response pattern translates into durable clinical benefit.

Questions clinicians ask

Who should be considered for this pathway?

The FDA indication applies to adults with previously untreated stage II or III locally advanced rectal cancer that is confirmed as MSI-H or dMMR. It should not be extrapolated to microsatellite-stable or mismatch repair-proficient disease, and treatment selection still requires accurate staging, biomarker confirmation and multidisciplinary assessment.

Does a complete clinical response mean the cancer is cured?

No. It means no residual tumor is detectable using the protocol’s clinical, endoscopic and imaging assessments. Because no surgical specimen is available to establish a pathologic complete response, continued surveillance is essential, and longer follow-up is needed to quantify local regrowth, distant recurrence and survival.

Can chemotherapy, radiation and surgery be omitted from the outset?

They can be deferred while dostarlimab is given in an eligible patient, with the goal of avoiding them if a complete response is sustained. They remain potential salvage or subsequent treatments when response is incomplete, disease progresses or regrowth occurs. The pathway therefore requires access to both intensive surveillance and conventional rectal cancer care.

What does accelerated approval mean for counseling?

It means the FDA judged the available response evidence sufficient for earlier access while confirmatory evidence is developed. Clinicians should explain both the organ-preservation opportunity and the remaining uncertainty about long-term recurrence, survival and rare toxicity. Continued approval can depend on verification of clinical benefit in additional or ongoing study.

References

1. FDA Grants Accelerated Approval to Dostarlimab for Locally Advanced Rectal Cancer — US Food and Drug Administration, 2026 2. PD-1 Blockade in Mismatch Repair–Deficient, Locally Advanced Rectal Cancer — The New England Journal of Medicine, 2022 3. ClinicalTrials.gov Study NCT04165772 — US National Library of Medicine, 2019