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First and only systemic therapy to improve survival when used before and after surgery for patients with MIBC who are ineligible for cisplatin-based chemotherapy
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First ever positive Phase 3 study in this cisplatin-ineligible patient population, representing significant advancement in MIBC
August 12, 2025--RAHWAY, N.J.--(BUSINESS WIRE)-- Merck (NYSE: MRK), known as MSD outside the United States and Canada, today announced positive topline results from the Phase 3 KEYNOTE-905 trial (also known as EV-303) in patients with muscle-invasive bladder cancer (MIBC) who are ineligible for cisplatin-based chemotherapy. In this study, KEYTRUDA® (pembrolizumab) plus Padcev (enfortumab vedotin-ejfv), given before and after surgery (radical cystectomy), demonstrated a statistically significant and clinically meaningful improvement in event-free survival (EFS), the study’s primary endpoint, as well as overall survival (OS) and pathologic complete response (pCR) rate, key secondary endpoints, compared to surgery (radical cystectomy) alone.
“Patients with muscle-invasive bladder cancer who are ineligible for cisplatin-based chemotherapy have not seen any treatment advance beyond surgery and face high rates of disease recurrence and a poor prognosis, even after having their bladder removed,” said Dr. Christof Vulsteke, MD, PhD, head of Integrated Cancer Center Ghent (IKG) and Clinical Trial Unit Oncology Ghent and KEYNOTE-905 principal investigator. “The KEYNOTE-905 study results mark the first time a systemic treatment approach, used before and after surgery, significantly extended survival over standard-of-care surgery in this population, demonstrating the potential of this combination to address a critical unmet need.”
The trial, evaluating Merck’s KEYTRUDA, an anti-PD-1 therapy, plus Padcev, an antibody-drug conjugate (ADC), was conducted in collaboration with Pfizer (previously Seagen) and Astellas and builds on the clinical success of this combination in locally advanced or metastatic urothelial cancer. The trial is continuing to evaluate the secondary EFS, OS, and pCR rate endpoints for neoadjuvant and adjuvant KEYTRUDA versus surgery alone as they continue to mature.
“There is a real and pressing need for more effective options for patients with bladder cancer who are ineligible for cisplatin-based treatment,” said Dr. Marjorie Green, senior vice president and head of oncology, global clinical development, Merck Research Laboratories. “The compelling survival results observed in this study reinforce the potential of combining KEYTRUDA with an antibody-drug conjugate to help address a significant unmet need in this vulnerable population.”
The safety profile of KEYTRUDA plus Padcev in this study was consistent with the known safety profiles of each agent. No new safety signals were identified with the combination. The companies plan to share these results with regulatory authorities worldwide and will present the data at an upcoming medical meeting.
KEYTRUDA plus Padcev is approved for the treatment of adult patients with locally advanced or metastatic urothelial cancer (la/mUC) in the U.S., the European Union (EU), Japan and several other countries around the world. KEYTRUDA as monotherapy is also approved in the U.S., EU, Japan and other countries for the treatment of certain patients with la/mUC or a type of non-muscle-invasive bladder cancer (NMIBC).
Five additional Phase 3 studies are currently evaluating KEYTRUDA across all stages of bladder cancer, including non-muscle-invasive, muscle-invasive and metastatic. Three of these studies are in MIBC including KEYNOTE-866 (NCT03924856), KEYNOTE-992 (NCT04241185) and KEYNOTE-B15 (NCT04700124), which is also known as EV-304 and is being conducted in collaboration with Pfizer and Astellas. KEYTRUDA is also being evaluated in combination with Bacillus Calmette-Guerin (BCG) in patients with NMIBC in the Phase 3 KEYNOTE-676 (NCT03711032) trial, and as adjuvant treatment in patients with localized muscle-invasive urothelial carcinoma and locally advanced urothelial carcinoma KEYNOTE-123 (NCT03244384).
About KEYNOTE-905/EV-303
KEYNOTE-905, also known as EV-303, is an open-label, randomized, multi-arm, controlled, Phase 3 trial (ClinicalTrials.gov, NCT03924895) evaluating perioperative KEYTRUDA, with or without Padcev, versus surgery alone in patients with MIBC who are either not eligible for or declined cisplatin-based chemotherapy. The trial enrolled 595 patients who were randomized to receive either:
Arm A: Three cycles of preoperative KEYTRUDA, followed by surgery to remove the bladder (radical cystectomy), followed by 14 cycles of postoperative KEYTRUDA;
Arm B: Surgery alone;
Arm C: Three cycles of preoperative KEYTRUDA plus enfortumab vedotin, followed by surgery to remove the bladder (radical cystectomy), followed postoperatively by six cycles of KEYTRUDA plus enfortumab vedotin and then eight cycles of KEYTRUDA alone.
The primary objective of this trial was to compare EFS between arm C and arm B, defined as the time from randomization to the first occurrence of any of the following events: progression of disease that precludes radical cystectomy (RC) surgery or failure to undergo RC surgery in participants with residual disease, gross residual disease left behind at the time of surgery, local or distant recurrence as assessed by imaging and/or biopsy or death due to any cause. The key secondary objectives were to compare OS and difference in pCR rate between arm C and arm B, as well as EFS, OS and the difference in pCR rate between arm A and arm B. The study remains ongoing to test hypotheses between arm A and arm B.
About bladder cancer
Bladder cancer is the ninth most common cancer worldwide, diagnosed in more than 614,000 patients each year globally. Muscle-invasive bladder cancer represents approximately 30% of all bladder cancer cases. The standard treatment for patients with MIBC is neoadjuvant cisplatin-based chemotherapy followed by surgery, which has been shown to prolong survival. However, up to half of patients with MIBC are not eligible to receive cisplatin and face limited treatment options, typically undergoing surgery alone.
About Merck’s early-stage cancer clinical program
Finding cancer at an earlier stage may give patients a greater chance of long-term survival. Many cancers are considered most treatable and potentially curable in their earliest stage of disease. Building on the strong understanding of the role of KEYTRUDA in later-stage cancers, Merck is studying KEYTRUDA in earlier disease states, with more than 25 ongoing registrational studies across multiple types of cancer.
About KEYTRUDA® (pembrolizumab) injection, 100 mg
KEYTRUDA is an anti-programmed death receptor-1 (PD-1) therapy that works by increasing the ability of the body’s immune system to help detect and fight tumor cells. KEYTRUDA is a humanized monoclonal antibody that blocks the interaction between PD-1 and its ligands, PD- L1 and PD-L2, thereby activating T lymphocytes which may affect both tumor cells and healthy cells.
Merck has the industry’s largest immuno-oncology clinical research program. There are currently more than 1,600 trials studying KEYTRUDA across a wide variety of cancers and treatment settings. The KEYTRUDA clinical program seeks to understand the role of KEYTRUDA across cancers and the factors that may predict a patient's likelihood of benefitting from treatment with KEYTRUDA, including exploring several different biomarkers.
About Merck
At Merck, known as MSD outside of the United States and Canada, we are unified around our purpose: We use the power of leading-edge science to save and improve lives around the world. For more than 130 years, we have brought hope to humanity through the development of important medicines and vaccines. We aspire to be the premier research-intensive biopharmaceutical company in the world – and today, we are at the forefront of research to deliver innovative health solutions that advance the prevention and treatment of diseases in people and animals. We foster a diverse and inclusive global workforce and operate responsibly every day to enable a safe, sustainable and healthy future for all people and communities.
About the Merck, Pfizer and Astellas collaboration
Merck previously entered a clinical collaboration agreement with Seagen and Astellas to evaluate the combination of Merck’s KEYTRUDA® (pembrolizumab) and Seagen’s and Astellas’ Padcev® (enfortumab vedotin-ejfv) in patients with muscle-invasive bladder cancer (MIBC) who are not eligible for or declined cisplatin-based chemotherapy. Pfizer Inc. successfully completed its acquisition of Seagen on December 14, 2023. Padcev® and the Padcev device are trademarks jointly owned by Agensys, Inc., and Seagen Inc. Pfizer Inc. completed its acquisition of Seagen on December 14, 2023.