A cancer drug that eliminated rectal tumors in every patient treated so far has received a landmark U.S. FDA Breakthrough Therapy Designation, putting it on a fast track toward wider availability. Dostarlimab, sold under the brand name Jemperli, achieved a 100% clinical complete response rate in a trial at Memorial Sloan Kettering Cancer Center — meaning no detectable tumors remained in any of the 42 participants who completed treatment.
At a glance
- Dostarlimab: A PD-1-blocking antibody that works by helping the immune system recognize and attack cancer cells, it eradicated rectal tumors without surgery, radiation, or chemotherapy in every participant of the MSK trial.
- Breakthrough Therapy Designation: Granted by the U.S. FDA to accelerate development of drugs for serious conditions with no comparable treatment available — only about 30–40% of requests receive it each year.
- Clinical complete response: Defined as complete pathologic response or no evidence of tumors confirmed by MRI, endoscopy, and digital rectal exam — achieved by all 42 patients in the trial, some now cancer-free for up to four years.
What makes this result so unusual
A 100% response rate in oncology is extraordinarily rare. Trials routinely celebrate drugs that work for a fraction of patients or that slow rather than reverse disease. Dostarlimab did something different.
The drug targets locally advanced dMMR/MSI-H rectal cancer, a subtype defined by a specific genetic mismatch repair deficiency found in roughly 5–10% of rectal cancer cases. That deficiency also happens to make tumors unusually visible to the immune system — which is exactly what PD-1-blocking antibodies like dostarlimab are designed to exploit.
MSK gastrointestinal oncologist Andrea Cercek, who led the trial, reported in June that all 42 patients who completed treatment showed no evidence of disease. “Most people on the trial have been free of cancer for at least a year,” she said, “and the original participants have been healthy for up to four years and counting. The success rate remains 100%.”
Why current treatments make this matter even more
Rectal cancer is not a rare diagnosis. In the U.S., roughly 46,220 people receive one each year. Standard treatment — surgery combined with radiation and chemotherapy — often works, but it leaves lasting consequences.
Survivors frequently face permanent colostomies, loss of fertility, bowel and bladder dysfunction, and sexual side effects. For younger patients especially, those outcomes can reshape the entire arc of a life. An immunotherapy that clears tumors while sparing patients surgery and radiation entirely would represent a profound shift in what recovery from this disease can look like.
“This new treatment is also proving very durable,” Cercek added. Side effects from dostarlimab were described as mild and well tolerated — a sharp contrast to the toxicity of conventional chemoradiation regimens.
What the FDA designation means in practice
Breakthrough Therapy Designation is not approval. It is a formal signal from the U.S. FDA that a drug addresses a serious unmet need and that the agency will work closely with developers to speed its review. As of June 2024, the FDA had received 1,516 such requests and granted only 587 — roughly one in three.
This is the second FDA designation dostarlimab has received. It was granted Fast Track status in January 2023 C.E. Breakthrough status goes further, providing more intensive FDA guidance and potentially cutting years from the path to market. Drugs with this designation can reach patients around three years sooner than those following the standard review timeline.
GlaxoSmithKline, which manufactures Jemperli, described the designation as supporting “a path to help change the treatment paradigm” for this patient population. The full trial results were published in The New England Journal of Medicine.
What still lies ahead
The trial cohort, while remarkable in its outcomes, remains relatively small at 42 patients — and all of them share the same rare genetic subtype. Larger, more diverse trials will be essential to confirm whether the results hold across a broader population and over longer time horizons. Researchers and regulators will also need to monitor long-term safety and assess whether dostarlimab’s promise extends to other cancer types driven by similar mismatch repair deficiencies, a question that the National Cancer Institute and other institutions are actively investigating.
Still, the combination of a 100% response rate, durable remissions now stretching past four years, and a formal FDA fast-track pathway gives oncologists and patients genuine reason for optimism. For a disease whose standard treatments can feel like trading one kind of suffering for another, dostarlimab points toward something better.
Read more
For more on this story, see: New Atlas
For more from Good News for Humankind, see:
- Alzheimer’s risk cut in half by drug in landmark prevention trial
- U.K. cancer death rates down to their lowest level on record
- The Good News for Humankind archive on global health
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