On August 12, 2025 Merck (NYSE: MRK), known as MSD outside the United States and Canada, reported 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 (Press release, Merck & Co, AUG 12, 2025, View Source [SID1234655107]). 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.

Schedule your 30 min Free 1stOncology Demo!
Discover why more than 1,500 members use 1stOncology™ to excel in:

Early/Late Stage Pipeline Development - Target Scouting - Clinical Biomarkers - Indication Selection & Expansion - BD&L Contacts - Conference Reports - Combinatorial Drug Settings - Companion Diagnostics - Drug Repositioning - First-in-class Analysis - Competitive Analysis - Deals & Licensing

                  Schedule Your 30 min Free Demo!

"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.