3 ESMO 2026 Results in Endometrial and Breast Cancer to Know

Several phase 3 trials presented at the European Society for Medical Oncology (ESMO) Congress 2026, held Oct. 23-27 in Madrid, focused on cancers that mainly affect women. Two brought new options for advanced endometrial cancer, and one gave final survival results for a breast cancer treatment many patients ask about. Here are three results to know.

1. Endometrial Cancer: Keytruda Alone Beat Chemo for dMMR Tumors

Some endometrial tumors are mismatch repair deficient (dMMR), meaning the cells cannot fix certain DNA copying mistakes, and these tumors tend to respond well to immunotherapy. The KEYNOTE-C93 trial compared Keytruda (pembrolizumab) alone with carboplatin and paclitaxel chemotherapy as a first treatment in 299 people with advanced or recurrent dMMR endometrial cancer. Patients on Keytruda went a median of 38.2 months before their cancer grew, compared with 8.4 months with chemotherapy, a 43% lower risk of the cancer growing or death. At three years, 70.7% vs. 62.0% were alive, a difference that was not statistically significant, and follow-up continues.

Keytruda was also easier to tolerate: serious treatment-related side effects happened in 18.1% of patients, compared with 50.7% on chemotherapy. Keytruda is approved for several uses in endometrial cancer, but using it alone as the first treatment for advanced dMMR disease is not yet an approved use.

2. Endometrial Cancer: A New Drug After Chemotherapy and Immunotherapy

When advanced endometrial cancer grows after both platinum chemotherapy and immunotherapy, options are limited. The TroFuse-005 trial compared the investigational drug sacituzumab tirumotecan (sac-TMT), an antibody-drug conjugate that delivers a cancer-killing drug to cells carrying a protein called TROP2, with doxorubicin or paclitaxel chemotherapy in 776 people in this situation. Patients who received sac-TMT lived a median of 19.0 months, compared with 12.1 months with chemotherapy, a 32% lower risk of death, and their tumors shrank about twice as often (35.1% vs. 17.3%).

Serious treatment-related side effects happened in 54.4% of patients on sac-TMT and 41.4% on chemotherapy, most often low blood counts and mouth sores. Sac-TMT is not approved; the U.S. Food and Drug Administration (FDA) is reviewing it, with a decision expected by June 15, 2027.

3. Breast Cancer: Final Survival Results for Verzenio After Another CDK4/6 Drug

CDK4/6 inhibitors are a standard part of treatment for hormone receptor (HR)-positive, HER2-negative advanced breast cancer, but the cancer often grows despite them. The postMONARCH trial tested whether switching to Verzenio (abemaciclib) plus Faslodex (fulvestrant) helps in 368 people whose cancer grew on another CDK4/6 inhibitor. Patients on Verzenio lived a median of 32.1 months, compared with 24.6 months with a placebo (inactive pill), but this difference was not statistically significant, meaning it may have been due to chance. Patients on Verzenio did go longer before needing chemotherapy, 13.6 vs. 9.7 months.

Serious side effects happened in 57.5% of patients on Verzenio and 23.2% on placebo, most often diarrhea and low white blood cell counts. The researchers noted the trial was designed mainly to measure time without cancer growth, not survival.

What's Still Unknown

Follow-up is still short for some of these trials, and survival results may change with time. In KEYNOTE-C93, the difference in survival between Keytruda and chemotherapy was not statistically significant at three years, so researchers will keep following patients to see whether Keytruda alone helps people live longer. In postMONARCH, the survival difference was also not statistically significant, so it is not certain that Verzenio helps people live longer in this setting.

The endometrial cancer results apply to specific groups, so tumor testing matters. KEYNOTE-C93 included only people with dMMR tumors, and TroFuse-005 included people whose cancer had grown after both chemotherapy and immunotherapy. Sac-TMT is still under FDA review, so it is not yet available outside of clinical trials.

What It Means for You

If you have advanced endometrial cancer, ask whether your tumor has been tested for dMMR, also called mismatch repair status. This test is done on a tumor sample and helps your care team choose among treatments, including immunotherapy. If your cancer has grown after chemotherapy and immunotherapy, ask whether a clinical trial of a newer drug might fit.

If you have HR-positive breast cancer that grew on a CDK4/6 inhibitor, ask your care team how these results fit with your other options. Patients on Verzenio went longer before needing chemotherapy, but they also had more serious side effects, including diarrhea and low white blood cell counts, so it helps to talk through the trade-offs before deciding.

References

1. "KEYTRUDA (pembrolizumab) as Monotherapy Reduced the Risk of Disease Progression or Death by 43% for Certain Patients With Advanced or Recurrent Endometrial Cancer With Mismatch Repair Deficient Tumors Compared to Chemotherapy." Merck. Oct. 26, 2026.
2. "Sacituzumab Tirumotecan (Sac-TMT) Reduced the Risk of Death by 32% and the Risk of Disease Progression or Death by 41% Compared to Chemotherapy in Certain Patients With Advanced or Recurrent Endometrial Cancer." Merck. Oct. 26, 2026.
3. Kalinsky K, Wander SA, Hamilton E, et al. "Overall survival from the phase III postMONARCH trial of abemaciclib plus fulvestrant versus placebo plus fulvestrant for HR+, HER2- advanced breast cancer following progression on a prior CDK4/6 inhibitor plus endocrine therapy." Annals of Oncology. Published online Oct. 24, 2026.

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