Update on phase III KEYNOTE-B21 trial evaluating Keytruda (pembrolizumab) + chemotherapy, with or without radiotherapy, for patients with newly diagnosed, high-risk endometrial cancer after surgery with curative intent

At a pre-specified interim analysis conducted by an independent Data Monitoring Committee, adjuvant treatment with Keytruda plus chemotherapy, with or without radiotherapy, did not meet the study’s pre-specified statistical criteria for DFS compared to placebo plus adjuvant chemotherapy, with or without radiotherapy. The study’s other primary endpoint of overall survival (OS) was not formally tested since superiority was not reached for DFS. The safety profile of Keytruda was consistent with that observed in previously reported studies; no new safety signals were identified. A full evaluation of the data from this study is ongoing. Merck will work with investigators to share the results with the scientific community.

“While these results were not what we had hoped, we are focused on continuing to build on the established role of Keytruda in advanced endometrial carcinoma through our approved indications, while rapidly progressing clinical research evaluating Keytruda based combinations and other investigational candidates, including antibody-drug conjugates, in endometrial and other types of gynecologic malignancies,” said Dr. Gursel Aktan, vice president, global clinical development, Merck Research Laboratories. “We would like to thank all the patients, the investigators and our study collaborators for their participation in this trial.”

In the U.S., Keytruda has two approved indications in endometrial cancer. One indication, based on KEYNOTE-775/Study 309, is in combination with Lenvima (lenvatinib), in collaboration with Eisai, for the treatment of patients with advanced endometrial carcinoma that is mismatch repair proficient (pMMR), as determined by an FDA-approved test, or not microsatellite instability-high (MSI-H), who have disease progression following prior systemic therapy in any setting and are not candidates for curative surgery or radiation. The second indication, based on KEYNOTE-158, is as a single agent, for the treatment of patients with advanced endometrial carcinoma that is MSI-H or mismatch repair deficient (dMMR), as determined by an FDA-approved test, who have disease progression following prior systemic therapy in any setting and are not candidates for curative surgery or radiation.

Merck has a comprehensive clinical development program in endometrial carcinoma, including the NRG-GY018/KEYNOTE-868 trial evaluating Keytruda in combination with standard of care chemotherapy (carboplatin and paclitaxel), followed by Keytruda as a single agent for the treatment of patients with primary advanced or recurrent endometrial carcinoma. As previously announced, the FDA has granted priority review for Merck’s supplemental Biologics License Application (sBLA) based on this study and has set a Prescription Drug User Fee Act (PDUFA), or target action, date of June 21, 2024.

The program also includes the KEYNOTE-C93 study evaluating Keytruda versus chemotherapy in dMMR advanced or recurrent endometrial carcinoma, as well as the MK-2870-005 study evaluating sacituzumab tirumotecan (sac-TMT), an investigational trophoblast cell-surface antigen 2 (TROP2)-directed antibody-drug conjugate (ADC) being developed in collaboration with Kelun-Biotech, compared to a treatment of physicians’ choice in patients with endometrial carcinoma who have received prior platinum-based chemotherapy and immunotherapy.