Merck drug extends survival in endometrial cancer, wins FDA priority review

On October 26, 2026, Merck presented Phase 3 trial results showing its experimental antibody-drug conjugate sacituzumab tirumotecan (sac-TMT), developed with Sichuan Kelun-Biotech, reduced the risk of death by 32% in advanced endometrial cancer, extending median survival to 19 months versus 12.1 months for chemotherapy. The U.S. FDA granted priority review with a decision expected by June 2027. Higher toxicity was noted, with 54% experiencing severe side effects. Analysts project overall sales up to $15 billion.

Phase 3 trial efficacy results

• ▪Sac-TMT reduced the risk of disease progression or death by 41%, extending progression-free survival to a median of 7.2 months versus 3.9 months for chemotherapy in advanced endometrial cancer
• ▪In a 776-patient Phase 3 study presented, Merck and Kelun-Biotech's sacituzumab tirumotecan (sac-TMT) reduced death risk by 32%, extending median survival to 19 months versus 12.1 months for chemotherapy in advanced endometrial cancer
• ▪Approximately 35% of advanced endometrial cancer patients treated with sac-TMT experienced tumor shrinkage, compared with 17% of patients receiving doctor-chosen chemotherapy doxorubicin or paclitaxel

Treatment safety and side effects

• ▪More than 54% of endometrial cancer patients receiving sac-TMT (sacituzumab tirumotecan) experienced severe treatment-related side effects such as anemia and mouth sores, compared with 41% on chemotherapy
• ▪Three patients in each treatment group died from treatment-related complications in the Phase 3 trial of sac-TMT in advanced endometrial cancer, and 3% of sac-TMT patients discontinued treatment due to side effects

Expansion into other cancer indications

• ▪In a study in China published in the New England Journal of Medicine, sac-TMT combined with Keytruda reduced the risk of disease progression or death by 51% in non-small cell lung cancer
• ▪Merck is pursuing sac-TMT across 18 late-stage studies globally, including trials in lung cancer and other common tumor types

Merck deal and strategic context

• ▪Merck acquired rights outside China to sac-TMT through a deal with discoverer Sichuan Kelun-Biotech Biopharmaceutical Co., targeting TROP2 protein common in endometrial tumors
• ▪Merck is advancing sac-TMT development to build revenue ahead of the 2028 patent expiration for its blockbuster immunotherapy Keytruda

Analyst commercial and revenue forecasts

• ▪Jefferies analysts project peak annual sales for sac-TMT (sacituzumab tirumotecan) of $900 million in endometrial cancer and $9 billion across all potential indications
• ▪HSBC analysts estimate that sac-TMT and its combination therapies represent a $12 billion to $15 billion commercial opportunity

Uterine cancer mortality

• ▪According to the American Cancer Society, approximately 68,000 U.S. women are expected to be diagnosed with uterine cancer in 2026, with over 14,000 deaths
• ▪Merck Research Laboratories President Dean Li stated that uterine cancer is one of the few cancers with an increasing mortality rate