54% Cure Potential with Dostarlimab in Endometrial Cancer: Long-Term RUBY Data
In this article
A Signal of Cure Potential with Dostarlimab in dMMR/MSI-H Endometrial Cancer: What Do the Long-Term RUBY Data Mean?
Why Is dMMR/MSI-H Endometrial Cancer So Sensitive to Immunotherapy?
Endometrial cancer is not a single disease. We now seek to understand it through its molecular subtypes as much as its histology, and often even more so. dMMR/MSI-H tumors are a very distinctive group in this respect. Defects in the DNA repair system cause numerous mutations to accumulate in these tumors. These mutations can make the tumor cell more “foreign” and recognizable to the immune system.
This biological characteristic explains why immune checkpoint inhibitors such as PD-1 inhibitors demonstrate particularly strong efficacy in dMMR/MSI-H endometrial cancer. Dostarlimab is an immunotherapy that targets PD-1. When given with chemotherapy, it can help the immune system develop a more lasting response against the tumor while reducing tumor burden.
Brief Concept Note: What Are dMMR and MSI-H?
dMMRmeans that mismatch repair, the system that repairs DNA mismatches, is defective. MSI-Hmeans high microsatellite instability; it indicates the accumulation of numerous errors in short repetitive regions of DNA. These two conditions often occur together and suggest that the tumor may be more sensitive to immunotherapy.
How Does Dostarlimab Work?
Dostarlimab is a monoclonal antibody that targets an immune checkpoint called PD-1. PD-1 is a braking mechanism found on T cells. Cancer cells can use this brake to evade the immune system. By releasing this brake, dostarlimab aims to enable T cells to act more effectively against tumor cells.
Because dMMR/MSI-H tumors contain numerous neoantigens, there are more biological markers for the immune system to target. PD-1 blockade therefore has a strong biological basis for producing not only temporary tumor shrinkage but also long-term remission in some patients in this group.
Adding Dostarlimab to Chemotherapy, Followed by Maintenance
In the RUBY / ENGOT-EN6-NSGO / GOG-3031 study, patients with primary advanced or recurrent endometrial cancer were randomized to receive dostarlimab or placebo together with carboplatin + paclitaxel chemotherapy as first-line treatment. After the chemotherapy period, dostarlimab maintenance continued every 6 weeks for up to 3 years.
A total of 494 patients were randomized; 118 of them had dMMR/MSI-H tumors. The initial NEJM publication showed a very substantial PFS advantage with the addition of dostarlimab in the dMMR/MSI-H group. The long-term analysis at ASCO 2026 evaluated whether this effect persisted after approximately 4,5 years of follow-up.
Brief Concept Note: What Does Maintenance Treatment Mean?
Maintenance treatmentis treatment given for a longer period after the initial intensive treatment has been completed, to maintain disease control and reduce the risk of recurrence. In the RUBY study, patients continued dostarlimab or placebo maintenance after chemotherapy.
| Item | Dostarlimab arm | Control arm | Clinical significance |
|---|---|---|---|
| Initial treatment | Dostarlimab + carboplatin + paclitaxel | Placebo + carboplatin + paclitaxel | Immunotherapy was added to the standard platinum-taxane chemotherapy backbone. |
| Maintenance period | Dostarlimab every 6 weeks for up to 3 years | Placebo | The aim was to sustain the response for a long time. |
| Total number of patients | 494 patients | A broad study population with primary advanced or recurrent endometrial cancer. | |
| Number of dMMR/MSI-H patients | 118 patients | The biological subgroup most sensitive to immunotherapy. | |
| Long-term follow-up | 55,6 months of median follow-up | The durability of responses and a possible plateau effect were evaluated. | |
4-Year PFS: 57,9% Versus 15,7%
In the ASCO 2026 analysis, the median follow-up duration was 55,6 months . In the dMMR/MSI-H patient group, the 4-year progression-free survival rate was reported as %57,9in the dostarlimab + chemotherapy arm, and as %15,7 in the placebo + chemotherapy arm. Median PFS was not reached in the dostarlimab arm; in the control arm it was 7,7 months . The hazard ratio for PFS was reported as 0,30 .
Brief Concept Note: What Are PFS and HR?
PFSmeans progression-free survival; it indicates the period during which the disease remains under control without progression or death. HRmeans hazard ratio, or risk ratio. An HR of 0,30 indicates that the risk of progression or death in the dostarlimab arm was approximately 70% lower than in the control arm.
Why Is This PFS Result So Important?
- Long-term plateau signal: The 4-year PFS remaining at 57,9% suggests that long-term disease control developed in a group of patients.
- Median PFS was not reached: Median PFS could not be calculated because more than half of the patients in the dostarlimab arm had not experienced a progression event.
- Substantial separation from the control arm: In the control arm, median PFS was 7,7 months and 4-year PFS was 15,7%.
- Few events during additional follow-up: The reporting of only 4 new progression events during approximately 2,5 years of additional follow-up after the initial PFS analysis is notable for the durability of responses.
4-Year Overall Survival: 72,8% Versus 40,3%
Overall survival data in the long-term analysis also strongly favored dostarlimab. In the dMMR/MSI-H patient group, the 4-year overall survival rate was reported as %72,8in the dostarlimab + chemotherapy arm and as %40,3 in the placebo + chemotherapy arm. The hazard ratio for OS was 0,34 ; this means an approximately 66% relative reduction in the risk of death.
Median OS was not reached in the dostarlimab arm; it was reported as 32,8 months in the control arm. The fact that approximately 71% of patients in the control arm received immunotherapy after progression makes the preservation of the survival advantage from giving dostarlimab in the first line even more meaningful.
Brief Concept Note: How Does Subsequent Immunotherapy Affect the Interpretation of OS?
If patients in the control arm can receive immunotherapy after the disease progresses, the overall survival difference between the two arms may generally diminish. The preservation of an OS advantage in the arm that used dostarlimab in the first line despite this strengthens the biological and clinical value of giving immunotherapy early.
| Outcome | Dostarlimab + chemotherapy | Placebo + chemotherapy | Effect measure | Clinical interpretation |
|---|---|---|---|---|
| 4-year PFS | %57,9 | %15,7 | HR 0,30 | Approximately 70% relative reduction in the risk of progression or death. |
| Median PFS | Not reached | 7,7 months | — | A signal of long-term disease control in the dostarlimab arm. |
| 4-year OS | %72,8 | %40,3 | HR 0,34 | Approximately 66% relative reduction in the risk of death. |
| Median OS | Not reached | 32,8 months | — | The overall survival curve remains strongly in favor of dostarlimab. |
| Estimated cure potential | %54 | %14 | 3,9-fold increase | Modeling suggests a substantial increase in the proportion of patients with a low long-term risk of progression. |
Mixture Cure Model: A Promising Concept That Requires Careful Use
One of the most striking terms in the long-term RUBY analysis is “cure potential.” The researchers evaluated patients' long-term risk of progression using a statistical method used in studies showing a long-term survival plateau, called the mixture cure model . According to this modeling, in patients with dMMR/MSI-H endometrial cancer, estimated cure potential was calculated as %54with dostarlimab + chemotherapy and as %14 in the chemotherapy-only arm.
Brief Concept Note: Cure Potential Does Not Mean Definite Cure
Cure potentialin this analysis refers to the proportion of patients estimated by a statistical model to have a low long-term risk of progression or disease-related death. This does not mean that every patient has definitely been cured. However, when survival curves develop a plateau, it suggests that some patients may remain disease-free for a long time and that the possibility of lasting remission may become realistic even in advanced disease.
Great balance is needed when explaining this concept to patients. Saying “definite cure” is not scientifically correct. However, saying “this treatment may produce a long-term response that can keep the disease under control for years in some patients and reduce the risk of recurrence to a very low level” more accurately reflects the spirit of the data.
RUBY's Effect Is Not Limited to dMMR/MSI-H, but the Strongest Signal Is in This Subgroup
Because of its sensitivity to immunotherapy, the dMMR/MSI-H subgroup is the patient group in which RUBY showed the most striking benefit. However, a survival advantage in favor of dostarlimab + chemotherapy was also reported in the overall study population. In the long-term data, median overall survival in the overall population was reported as 44,6 monthsin the dostarlimab + chemotherapy arm and as 28,2 months in the control arm.
Although this finding suggests that RUBY's clinical effect is not confined to the dMMR/MSI-H group, the biological and clinical strength of treatment is seen most clearly in dMMR/MSI-H tumors. In patients with pMMR, meaning an intact mismatch repair system, the magnitude of immunotherapy benefit, patient selection, and combination strategies should be discussed more carefully.
Brief Concept Note: What Is pMMR?
pMMRmeans that the mismatch repair system is intact. In these tumors, the DNA repair system is relatively functional, and the mutation burden is generally not as high as in dMMR/MSI-H tumors. Sensitivity to immunotherapy may therefore be more variable.
From Chemotherapy to the Era of Molecularly Selected Immunotherapy in Endometrial Cancer
For many years, carboplatin-paclitaxel chemotherapy was the main systemic treatment for advanced or recurrent endometrial cancer. This treatment can produce an initial response in many patients, but disease control is often not lasting. With the introduction of molecular classification into clinical practice, endometrial cancer began to be evaluated not only through histology and stage but also through biological characteristics such as MMR/MSI status, POLE mutation, p53 status, and hormone receptors.
RUBY and similar studies showed that combining immunotherapy with chemotherapy early, particularly in dMMR/MSI-H patients, can change the treatment goal. In this group, the aim is now not merely to delay progression for a few months, but to achieve long-term remission and the potential to permanently change the natural course of the disease in some patients.
| Era / approach | Main treatment rationale | Strength | Limitation | What changed with RUBY |
|---|---|---|---|---|
| Chemotherapy era | Carboplatin + paclitaxel | Applicable to a broad patient group and can produce an initial response | The response is often not lasting; dMMR/MSI-H biology is not specifically targeted | Chemotherapy is now biologically strengthened with immunotherapy. |
| Single-agent immunotherapy era | PD-1 blockade in dMMR/MSI-H recurrent disease | Durable responses in selected patients | Often used in a later line | RUBY demonstrates the value of moving immunotherapy into the first line. |
| Chemotherapy + immunotherapy era | Platinum-taxane + PD-1 inhibitor in the first line | Substantial long-term advantage in PFS and OS | Immune adverse effects, patient selection, and treatment duration require attention | A signal of a long-term plateau and cure potential is emerging in dMMR/MSI-H patients. |
| Molecular personalization era | Treatment according to MMR/MSI, POLE, p53, and other biomarkers | The right treatment intensity for the right patient | Access to testing and standardized interpretation are needed | Molecular testing at diagnosis is now becoming central to treatment decisions. |
MMR/MSI Testing at Diagnosis Is Becoming Essential
The most practical message of the long-term RUBY data is this: in advanced or recurrent endometrial cancer, MMR/MSI status must be known at diagnosis. In dMMR/MSI-H patients, the treatment strategy is shifting from the goal of temporary control with chemotherapy alone to long-term disease control supported by immunotherapy.
MMR/MSI testing is important not only for treatment selection but also for evaluating the possibility of Lynch syndrome. Genetic counseling and germline testing may be considered, particularly in patients diagnosed at a young age or with a family history.
Practical Clinical Messages
- MMR/MSI testing at diagnosis: It is the foundation of treatment decisions in advanced or recurrent endometrial cancer.
- A strong standard in dMMR/MSI-H patients: Dostarlimab + carboplatin-paclitaxel is a core first-line strategy because of its long-term PFS and OS advantage.
- The maintenance period matters: Dostarlimab maintenance after chemotherapy should be considered part of long-term control.
- Cure potential should be explained carefully: It means an increase in the proportion of patients with a low long-term risk of progression, rather than definite cure.
- Monitoring for adverse effects is needed: Immune-related toxicities should be monitored during and after treatment.
Brief Concept Note: What Is Lynch Syndrome?
Lynch syndromeis an inherited syndrome that increases the risk of certain cancers, particularly colon and endometrial cancer, because of inherited defects in DNA repair genes. Genetic counseling should be considered according to the clinical context in patients found to have dMMR/MSI-H tumors.
Immunotherapy Can Provide Long-Term Benefit, but Requires Long-Term Follow-Up
Because dostarlimab is a PD-1 inhibitor, it requires careful monitoring for immune-related adverse effects. These effects can affect the skin, bowel, liver, lungs, thyroid, pituitary, kidneys, and other organs. Most adverse effects can be managed when recognized early, but may become serious if recognition is delayed.
Practical Note on Managing Adverse Effects
- Thyroid and endocrine system: TSH, free T4, glucose, and clinical fatigue should be closely monitored.
- Bowel: Diarrhea, abdominal pain, and bloody stools are important indicators of immune-mediated colitis.
- Lungs: A new cough or shortness of breath should be evaluated for immune-mediated pneumonitis.
- Liver: Increases in AST, ALT, and bilirubin should be monitored for immune-mediated hepatitis.
- Long-term maintenance: Patients should be informed that immune adverse effects may appear late, even after treatment has ended.
Brief Concept Note: What Is an Immune-Related Adverse Effect?
An immune-related adverse effectoccurs when immunotherapy overactivates the immune system, causing inflammation in healthy tissues. Conditions such as colitis, hepatitis, pneumonitis, thyroiditis, and hypophysitis may occur. Early diagnosis and corticosteroid treatment when necessary may be lifesaving.
How Should We Talk to the Patient?
“If your tumor is dMMR/MSI-H, your chance of substantial and long-lasting benefit from immunotherapy may be higher. The long-term results of the RUBY study show that adding dostarlimab to chemotherapy can keep the disease under control for years in some patients. However, ‘cure potential’ does not mean definite recovery; it describes an increased possibility of long-term disease control. Regular follow-up for adverse effects related to the immune system is needed during treatment.”
Treatment Goals Can Be Considered More Ambitiously in dMMR/MSI-H Disease
Academic Assessment
The long-term RUBY data show that, in dMMR/MSI-H endometrial cancer, we should now view immunotherapy not only as a treatment approach that controls disease but also as one that offers hope of long-term remission in some patients.
The 4-year PFS reaching 57,9% and the modeled estimate of 54% cure potential allow us to reconsider our treatment goals in this biological subgroup more ambitiously, but on a scientific basis.
In the future, endometrial cancer treatment will be shaped by earlier, more accurate, and more personalized immunotherapy strategies according to MMR/MSI status.
Who Will Actually Achieve Long-Term Remission?
The long-term RUBY data are very strong; however, the next goal is to better identify which patients will obtain this lasting benefit. dMMR/MSI-H status is a strong biomarker, but even within this group there are patients who can show primary resistance or early progression. Conversely, some patients may develop responses lasting for years.
Open Questions
- Resistance biology: What resistance mechanisms are present in patients who develop early progression despite being dMMR/MSI-H?
- Additional biomarkers: Can TMB, neoantigen burden, the immune microenvironment, POLE status, and ctDNA response better predict long-term benefit?
- Maintenance duration: Is dostarlimab maintenance for up to 3 years optimal, or is a shorter or longer duration needed?
- Treatment discontinuation strategy: When can treatment be safely stopped in patients who remain progression-free for a long time?
- Real-world data: Will this long-term benefit be preserved in older patients, those with comorbidities, or those with a vulnerable performance status?
- pMMR disease: How should combinations be developed to increase immunotherapy benefit in the pMMR subgroup?
Truecheck Note
The term “cure potential” in this study is an estimate obtained through statistical modeling; it does not mean that patients have definitely been cured. However, it strongly suggests that long-term disease control in advanced or recurrent dMMR/MSI-H endometrial cancer has now become a more realistic clinical goal.
Long-Term RUBY Data Made the Power of Immunotherapy Lasting in dMMR/MSI-H Endometrial Cancer
The long-term RUBY data presented at ASCO 2026 show that, in dMMR/MSI-H primary advanced or recurrent endometrial cancer, the combination of dostarlimab + carboplatin-paclitaxel does more than delay progression early on; it can provide long-term disease control. The reported results were 4-year PFS of 57,9% versus 15,7%, PFS HR 0,30; and 4-year OS of 72,8% versus 40,3%, OS HR 0,34.
Even more striking is that the mixture cure model estimated cure potential at 54% in the dostarlimab arm and 14% in the control arm. Although this term does not mean definite cure, it shows that a low long-term risk of progression and the possibility of lasting remission can now be discussed as realistic goals for some patients with advanced endometrial cancer.
The clearest message for clinical practice is this: in advanced or recurrent endometrial cancer, MMR/MSI testing should be performed at diagnosis; in dMMR/MSI-H patients, dostarlimab + carboplatin-paclitaxel followed by dostarlimab maintenance should be considered a core treatment strategy aimed at long-term survival and disease control. These data once again show that molecular personalization in endometrial cancer treatment is now central to treatment success, rather than optional.
References
- ASCO 2026 Abstract 5501. Long-term survival rates and cure modeling with dostarlimab plus chemotherapy in dMMR/MSI-H primary advanced or recurrent endometrial cancer in the ENGOT-EN6-NSGO/GOG-3031/RUBY trial.
- CancerNetwork. Dostarlimab Plus Chemotherapy Yields Curative Potential in dMMR/MSI-H Endometrial Cancer. 29 May 2026.
- Mirza MR et al. Dostarlimab for Primary Advanced or Recurrent Endometrial Cancer. New England Journal of Medicine. 2023.
- Powell MA et al. Overall survival in patients with endometrial cancer treated with dostarlimab plus carboplatin-paclitaxel in the randomized ENGOT-EN6-NSGO/GOG-3031/RUBY trial. Annals of Oncology. 2024.
- Powell MA et al. Efficacy and safety of dostarlimab in combination with carboplatin-paclitaxel in dMMR/MSI-H advanced or recurrent endometrial cancer. Gynecologic Oncology. 2025.
- ClinicalTrials.gov. RUBY / ENGOT-EN6 / GOG-3031. NCT03981796.
Was this article helpful?
Your feedback helps us improve our content.
Reader comments
Share your comment
Your name and comment are published only after administrator approval. Your email address is never shown to visitors.
Be the first to comment.