It was supported primarily by AZUR-1, an international clinical trial in 154 previously untreated patients. According to the FDA, 110 participants, or 71%, received dostarlimab alone without additional cancer treatment or disease progression during the study assessment period. The trial also recorded sustained complete clinical responses in a substantial, unspecified proportion of patients, but the 71% figure should not be interpreted as the proportion who achieved complete responses or remained cancer-free indefinitely.

The approval follows clinical studies led by gastrointestinal oncologists Luis Diaz Jr. and Andrea Cercek at Memorial Sloan Kettering Cancer Center. An initial trial, reported in The New England Journal of Medicine on June 5, 2022, enrolled 12 patients with rectal cancer. All 12 experienced a complete clinical response after treatment with dostarlimab alone, defined in the release as no detectable evidence of cancer.

None required chemotherapy, radiation or surgery during the initial study follow-up. This small, selected trial generated evidence that some rectal cancers with the relevant molecular features could respond without conventional treatment, but its size and limited follow-up did not establish how often the effect would occur in the wider patient population. An expanded phase 2 study published in The New England Journal of Medicine on April 27, 2025, and presented at the American Association for Cancer Research Annual Meeting tested immunotherapy in a broader group of 103 patients with stage I to III cancers.

The cohort included 49 patients with rectal cancer and 54 with gastroesophageal, hepatobiliary, colon, genourinary or gynecologic cancers. Approximately 80% of participants in the expanded study avoided surgery after immunotherapy. These findings broadened the clinical evidence beyond rectal cancer, but the FDA’s 2026 action was based primarily on AZUR-1, the larger rectal-cancer trial.

The indication therefore applies to adults with stage II or III disease whose tumors are MSI-H or dMMR, rather than to all forms of rectal cancer. AZUR-1 enrolled 154 patients with previously untreated stage II or III MSI-H or dMMR locally advanced rectal cancer. Its principal reported assessment found that 110 patients, or 71%, received dostarlimab without additional cancer treatment and without disease progression during the study assessment period.

The trial also showed sustained complete clinical responses in a substantial proportion of participants, although the supplied evidence does not specify the number in that sustained-response group. Continued clinical follow-up and confirmatory research will be required to establish the treatment’s long-term benefits. The reported results support the approved use in the selected population, while the available summary does not quantify durable remission for every participant or establish identical outcomes across all subgroups.

MSI-H and dMMR tumors have genetic characteristics that make them particularly responsive to certain immunotherapies, which help the immune system recognize and attack cancer cells. The treatment works within a selected molecular subgroup rather than serving as a general treatment for all locally advanced rectal cancers. That distinction is central to interpreting both the trial and the approval: the 71% AZUR-1 outcome applies to the biomarker-defined population studied, and the evidence does not establish that every person with MSI-H or dMMR locally advanced rectal cancer will respond to dostarlimab.

It also does not indicate that the same rate of response or avoidance of conventional treatment would be expected in cancers without those tumor characteristics. Rectal cancer has often been treated with chemotherapy, radiation and major surgery. The supplied news release notes that these interventions can result in permanent colostomies, infertility, incontinence and other lasting complications, including effects on bowel, bladder and sexual function and the ability to maintain normal daily activities.

Dostarlimab offers eligible patients the possibility of avoiding those treatments while preserving the rectum and potentially maintaining quality of life. This is a potential benefit of a complete response, not a guarantee for every participant, and the release does not provide a controlled comparison of quality-of-life outcomes between treatment groups. The extent and durability of that benefit must be assessed through continued follow-up and confirmatory research.

Cercek said the study showed that immunotherapy can replace surgery, radiation and chemotherapy for mismatch repair-deficient solid tumors, which could help patients preserve their organs and avoid the harsh side effects of chemotherapy and radiation. She also emphasized the importance of patients returning to their daily routines and maintaining independence. The release reported that several patients in the research later became pregnant and had children after treatment, describing these outcomes as unheard of with previous treatments for these cancers.

These are reported individual experiences within the research cohort; the supplied evidence does not provide a comparative measure of fertility, pregnancy rates or reproductive outcomes against another treatment. Swim Across America provided grant funding for the early research and subsequent clinical trials through its support of the Swim Across America Lab at Memorial Sloan Kettering, including grants associated with its Long Island Sound, Nassau-Suffolk and Fairfield County swims. Diaz said those grants were critical to the initial study and to advancing the trial into phase 2.

The nonprofit said it has supported immunotherapy research at Memorial Sloan Kettering since 1987 and that its funding helped advance four previously approved immunotherapies: ipilimumab, or Yervoy; nivolumab, or Opdivo; pembrolizumab, or Keytruda; and atezolizumab, or Tecentriq. Dostarlimab became the fifth FDA-approved immunotherapy on the organization’s list. Research associated with the dostarlimab trials also received support from the National Institutes of Health, National Cancer Institute, Stand Up To Cancer and other partners, while GSK supplied the medicine used in the studies.

Swim Across America’s role was primarily grant support for early research and the clinical trial program, rather than the conduct of AZUR-1 or the FDA regulatory review. The organization has raised more than $150 million since its founding in 1987, supports more than 60 cancer research projects annually and maintains 10 named labs at major research institutions. Its annual charity swims take place in 27 U.S. communities and involve thousands of swimmers, volunteers, donors and Olympians.

The funding history provides context for the development of the therapy, but the clinical findings, not the source of support, form the basis of the approval and its scope for patients with MSI-H or dMMR locally advanced rectal cancer. The sequence of evidence shows how a promising observation can be tested at increasing scale. The 2022 trial documented complete clinical responses in all 12 selected rectal cancer patients, the 2025 phase 2 study expanded the population to 103 participants across several solid-tumor types and found that approximately 80% avoided surgery, and AZUR-1 supplied the larger, disease-specific patient series supporting the FDA decision.

Accelerated approval reflects the strength of these results for the indicated population, but longer follow-up remains necessary to characterize the durability of tumor control and the full benefits and limitations of treatment. For eligible adults with stage II or III locally advanced rectal cancer and MSI-H or dMMR tumors, the approval establishes dostarlimab as an authorized option; it does not make the early response rates permanent or universal.

Subject of Research: Clinical evaluation of dostarlimab for biomarker-defined locally advanced rectal cancer.

Article Title: Swim Across America-funded cancer research leads to landmark FDA approval of immunotherapy for rectal cancer

Article References: Swim Across America-funded cancer research leads to landmark FDA approval of immunotherapy for rectal cancer. Original publication (Bibliographic details unavailable.)

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DOI: Not provided

Keywords: dostarlimab, rectal cancer, FDA approval, immunotherapy, AZUR-1, MSI-H, dMMR, clinical trial, Memorial Sloan Kettering, quality of life, Swim, Across