RAHWAY, N.J., Dec. 17, 2025 — Merck (NYSE: MRK) announced positive topline results from the Phase 3 KEYNOTE-B15 (EV-304) clinical trial, showing that KEYTRUDA® (pembrolizumab) combined with Padcev® (enfortumab vedotin-ejfv) significantly improved event-free survival (EFS), overall survival (OS), and pathologic complete response (pCR) rates in cisplatin-eligible patients with muscle-invasive bladder cancer (MIBC). Administered as neoadjuvant and adjuvant therapy before and after surgery, the regimen outperformed standard cisplatin-based chemotherapy and surgery, positioning it as the first perioperative immunotherapy plus ADC combination to demonstrate survival benefit in this population.
Science Significance
The KEYNOTE-B15 results represent a major scientific advance in perioperative oncology, validating the synergistic potential of combining immune checkpoint inhibition with an antibody-drug conjugate (ADC) in curative-intent bladder cancer. KEYTRUDA, an anti-PD-1 monoclonal antibody, enhances T-cell mediated anti-tumor immunity, while Padcev, an ADC targeting Nectin-4, delivers a cytotoxic payload directly to tumor cells. This dual mechanism addresses both immune evasion and tumor cell survival, resulting in deeper responses. The observed improvement in pathologic complete response, a recognized surrogate for long-term outcomes, underscores the regimen’s ability to fundamentally alter disease biology when introduced earlier in the treatment continuum.
Regulatory Significance
From a cGxP and regulatory affairs perspective, the findings provide strong support for global regulatory filings and potential label expansion. Demonstrating statistically significant improvements across primary and key secondary endpoints strengthens the evidentiary package required by health authorities. Combination regimens involving biologics and ADCs demand robust manufacturing controls, validated combination safety data, and integrated pharmacovigilance systems. The clean safety profile reported, consistent with known profiles of each agent, reinforces confidence in the quality, safety, and compliance frameworks underpinning the program and supports engagement with regulators worldwide.
Business Significance
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Commercially, the success of KEYTRUDA plus Padcev highlights the strategic importance of combination lifecycle management for established oncology brands. Expanding use into earlier, surgically curable disease stages significantly broadens the addressable market and strengthens long-term franchise value. Conducted in collaboration with Pfizer and Astellas, the trial exemplifies how cross-company partnerships can accelerate innovation while sharing development risk. Strong survival data also enhance the therapy’s positioning in payer and reimbursement discussions, as health systems increasingly prioritize treatments that deliver clear, durable survival advantages.
Patients’ Significance
For patients with muscle-invasive bladder cancer, the results address a critical unmet need. Despite standard cisplatin-based chemotherapy and surgery, nearly half of patients experience recurrence, often with poor prognosis. The ability of KEYTRUDA plus Padcev to significantly extend event-free and overall survival offers patients a realistic opportunity for longer remission and improved long-term outcomes. Higher pCR rates suggest more complete tumor eradication prior to surgery, which may translate into reduced relapse risk and improved quality of life, making this regimen a potentially transformative option for eligible patients.
Policy Significance
At the policy level, the findings support evolving frameworks that encourage earlier adoption of high-impact cancer therapies. As healthcare systems move toward value-based oncology care, treatments demonstrating meaningful survival benefit in earlier disease settings align with policy goals of reducing recurrence, downstream treatment costs, and long-term morbidity. The trial also reinforces the importance of innovation-friendly regulatory pathways that enable timely evaluation of complex combination therapies while maintaining rigorous standards for safety, efficacy, and quality.
The positive Phase 3 results from KEYNOTE-B15 position KEYTRUDA® plus Padcev® as a potential new perioperative standard of care for cisplatin-eligible patients with muscle-invasive bladder cancer. By integrating immunotherapy and ADC science within a rigorously controlled, cGxP-aligned clinical development program, the combination exemplifies how pharmaceutical innovation can redefine outcomes in high-risk cancers. As regulatory submissions advance and data are shared with health authorities, this milestone reinforces the role of science-driven pharma innovation in delivering durable survival benefits for patients.
Source: Merck press release
