Spanish hospital Valdecilla has participated in an international trial showing a cancer immunotherapy can completely eliminate tumors of the rectum in 76% of patients, sparing them from the life-altering consequences of surgery, chemotherapy, and radiation.
The significance of these findings, presented at the European Society for Medical Oncology (ESMO) 2026 congress in Madrid, lies in its potential to preserve quality of life. The standard of care for locally advanced rectal cancer involved multi-modal treatment that often led to permanent side effects, including the need for a colostomy bag, urinary and sexual dysfunction, and infertility.
Targeted Mechanism and High Efficacy in a Specific Cohort
The trial, known as Azur-1, is an international clinical trial of the highest level, in which the Cantabrian hospital participated alongside 39 other specialized centers from ten countries. The trial’s primary goal was to assess the efficacy of dostarlimab—a monoclonal antibody—in patients with locally advanced rectal cancer exhibiting tumors described as unstable, with a deficiency of the DNA repair protein, a specific genetic alteration that prevents them from adequately repairing DNA damage, leading to an accumulation of mutations.
Cancer Disappears Without Surgery or Chemotherapy
- It only works for patients whose rectal cancer has a specific genetic flaw (a deficiency of the DNA repair protein), affecting about 5% of cases.
- The drug, dostarlimab, gives a patient’s own immune system the weapons to defend itself against the tumor, with the cancer disappearing completely without surgery or chemotherapy.
- While initial results are outstanding, with a 76% complete response rate, more long-term data is needed: cure cannot yet be declared because there is still no long-term follow-up.
Drug Authorized in the United States
Dostarlimab has already been authorized in the United States.
“The fact that, to date, no recurrences of the disease have been observed after more than two years of follow-up should give healthcare professionals confidence in a strategy of organ preservation for this patient population.”
Transparency in Funding and Clinical Data
Dostarlimab is developed by the pharmaceutical company GSK, which will market it under the brand name Jemperli. The trial was conducted across 40 specialized centers in 10 countries, with four of the 144 participants being treated at Valdecilla Hospital in Cantabria, Spain. The "76% efficacy" figure represents the proportion of patients in the study who achieved a complete response. In total, 110 of the 144 participants saw the cancer disappear completely, and so far, after a median follow-up of more than two years, no relapses have occurred. Among them, the majority (68%) avoided surgery during the first year without the cancer reappearing, and twelve patients who were operated on have shown no signs of disease either.
Safety Profile and Known Adverse Reactions
While the efficacy data is highly promising, any medical intervention carries potential risks. The Azur-1 trial reported that the safety profile of the drug was, in general, consistent with the profile already known in solid tumors. Relevant adverse events occurred in 20% of patients. The most common side effects were fatigue (32%), skin rash (22%), diarrhea (18%), and itching (17%).
| Key Data from Azur-1 Trial | Statistic |
|---|---|
| Number of Patients Enrolled | 144 |
| Complete Response Rate (Efficacy) | 76% |
| Rate of Relevant Adverse Events | 20% |
| Most Frequent Adverse Events | Fatigue (32%), Rash (22%), Diarrhea (18%) |
| Treatment Discontinuation due to Adverse Events | 3% |
Oncologists Stress Cure Cannot yet Be Declared
While the absence of disease recurrence after a median follow-up of over two years is highly encouraging, oncologists stress that a cure cannot yet be declared, because there is still no long-term follow-up.
References
- European Society for Medical Oncology (ESMO). “ESMO 2026 Congress.”
- GlaxoSmithKline. “Jemperli (dostarlimab).”
