Merck's experimental cancer medicine sacituzumab tirumotecan extended median overall survival to 19 months, compared with 12.1 months for chemotherapy, in a Phase 3 trial involving patients with advanced or recurrent endometrial cancer who had already received two major types of treatment.
The findings, announced on October 26, 2026, come from the 776-patient TroFuse-005 trial. The medicine, also known as sac-TMT, significantly improved both overall survival and the time patients lived without their cancer worsening, according to results presented at the European Society for Medical Oncology (ESMO) Congress 2026 and published in The Lancet.
The results offer evidence of another potential treatment option for patients whose cancer has progressed after platinum-based chemotherapy and immunotherapy. However, serious treatment-related side effects were more frequent with sac-TMT, and the drug remains investigational in the United States.
As Reuters reported, the U.S. Food and Drug Administration has accepted an application for priority review of the medicine following the trial's survival findings.
What the Phase 3 Trial Found
The TroFuse-005 study randomly assigned 386 patients to sac-TMT and 390 to the physician's choice of two established chemotherapy drugs, doxorubicin or paclitaxel. The international, open-label trial evaluated patients who had previously received platinum-based chemotherapy and treatment targeting the PD-1 or PD-L1 immune pathways.
With a median follow-up of 14 months, researchers reported these findings:
- Overall survival: Median survival was 19.0 months with sac-TMT versus 12.1 months with chemotherapy, a difference of 6.9 months.
- Progression-free survival: Patients receiving sac-TMT had a median of 7.2 months before cancer progression or death, compared with 3.9 months in the chemotherapy group.
- Tumor response: An objective response was recorded in 35.1% of patients receiving sac-TMT versus 17.3% receiving chemotherapy.
The estimated hazard of death during follow-up was 32% lower in the sac-TMT group, with a hazard ratio of 0.68. The estimated hazard of cancer progression or death was 41% lower, with a hazard ratio of 0.59. Both primary results were statistically significant.
These percentages need careful interpretation. A 32% lower hazard of death does not mean that 32% more patients were cured or that every patient gained nearly seven months of life. Median survival describes the point at which half of the patients in a study group have died; it does not predict how long an individual patient will live.
Detailed results were provided in Merck's October 26 clinical announcement. The company is developing sac-TMT in collaboration with Kelun-Biotech.
Which Patients Could the Findings Affect?
Endometrial cancer develops in the lining of the uterus. Although many cases are diagnosed before the disease has spread, treatment becomes more challenging when cancer is advanced, returns after treatment, or continues progressing despite earlier therapies.
TroFuse-005 specifically studied patients who had already received platinum-based chemotherapy and PD-1/PD-L1 immunotherapy. Its results therefore cannot automatically be applied to people with newly diagnosed, early-stage disease or those who have not received these previous treatments.
Sac-TMT belongs to a class of medicines called antibody-drug conjugates. These treatments combine an antibody designed to recognize a particular cellular target with a powerful cancer-killing payload.
In this case, the medicine targets TROP2, a protein that is expressed at elevated levels in many tumor cells. The antibody component is designed to help deliver its drug payload toward cells expressing that target. This approach does not guarantee that the treatment will affect only cancer cells, which is one reason safety outcomes remain important.
The findings are particularly relevant because treatment choices can become limited after advanced endometrial cancer progresses despite chemotherapy and immunotherapy. Researchers are investigating whether sac-TMT could provide another option in that setting.
What Are the Side Effects and Limitations?
The survival improvement was accompanied by a substantial incidence of treatment-related adverse events.
Grade 3 or higher treatment-related adverse events occurred in 54.4% of patients receiving sac-TMT, compared with 41.4% of patients receiving chemotherapy. Grade 3 events are considered severe under standard clinical-trial toxicity grading.
Among patients receiving sac-TMT, commonly reported Grade 3 or higher adverse events included anemia (23.7%), neutropenia, or low levels of certain infection-fighting white blood cells (20.1%), and oral mucositis or stomatitis, involving inflammation or sores in the mouth (9.9%).
Treatment-related adverse events led to discontinuation in 3.1% of patients receiving sac-TMT and 4.9% of patients receiving chemotherapy. Three treatment-related deaths were reported in each group, equivalent to approximately 0.8% of patients in the respective safety populations.
The percentages for severe treatment-related events should not be confused with severe events from any cause. In the published trial results, Grade 3 or higher adverse events regardless of attribution occurred in 69% of sac-TMT recipients and 57% of chemotherapy recipients.
These findings underscore the importance of weighing potential survival benefits against adverse effects, other available treatment options and individual circumstances under specialist medical care.
The trial also has limitations. Its reported findings came from a prespecified interim analysis, with 14 months of median follow-up. Longer observation may provide a fuller understanding of survival, delayed side effects and the durability of treatment benefits.
In addition, the trial was open-label, meaning patients and investigators knew which treatment was being given. Although overall survival is an objective endpoint, knowledge of treatment assignment can influence some aspects of care and assessment.
The study directly compared sac-TMT with doxorubicin or paclitaxel. It did not establish that the investigational medicine is superior to every other possible treatment for advanced endometrial cancer.
What Happens Next With FDA Review?
The FDA has accepted Merck's Biologics License Application for priority review of sac-TMT in adults with endometrial cancer previously treated with platinum-containing chemotherapy and a PD-1 or PD-L1 inhibitor, administered either separately or together.
The agency has set June 15, 2027, as its target action date.
Priority review means the FDA intends to evaluate the application on an accelerated review timetable because the treatment may offer a meaningful improvement over existing options. It does not mean that the agency has approved the drug or determined that its benefits outweigh its risks for the proposed indication.
As of October 28, 2026, U.S. approval for this indication had not been established, and routine commercial availability had not been confirmed. The review process must still assess the submitted evidence, including effectiveness, safety and manufacturing information.
The next major milestone is the FDA's decision, which could determine whether sac-TMT becomes an additional treatment option for eligible patients in the United States. Longer-term clinical results and further safety monitoring will also help clarify its potential place in endometrial cancer care.
For now, TroFuse-005 provides randomized clinical evidence of improved survival in a specific group of previously treated patients, while the medicine's regulatory status and its long-term benefit-risk profile remain important considerations.
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