Merck (MRK) Initiates Phase 1/2 Clinical Trial in Japan for Keytruda in Pediatric Cancer and Merkel Cell Carcinoma
Strategic Clinical Trial Commences to Expand into Unapproved Areas in Japan
Merck & Co., Inc. (MRK) has begun recruiting patients for a Phase 1/2 clinical trial (KEYNOTE-G21) in Japan to expand the indications of its immuno-oncology drug, Keytruda (pembrolizumab). This trial targets patients with Merkel Cell Carcinoma (MCC) and pediatric solid tumors, indications that have been approved by the U.S. Food and Drug Administration (FDA) but not yet by the Japanese Pharmaceuticals and Medical Devices Agency (PMDA). The company aims to proactively secure pharmacokinetic (PK) and safety data from Japanese patients to overcome regulatory hurdles and gain approval.
Targeting Areas with High Unmet Medical Needs, Including Pediatric Rare Cancers
The first part (Arm 1) of this trial will focus on pediatric solid tumors and recurrent/refractory classical Hodgkin Lymphoma (cHL) patients, who have limited treatment options. The second part (Arm 2) will enroll adult MCC patients who have not received prior treatment, to evaluate the clinical efficacy of Programmed Death-1 (PD-1) receptor inhibition. This initiative aims to provide new standard treatment options for pediatric rare cancers and aggressive skin cancer, MCC, while also securing a foothold in a niche market.
Competition with Pfizer's Avelumab in the Local Market
Currently, the Japanese market for MCC treatment is dominated by Avelumab (Bavencio), co-developed by Pfizer (PFE) and Merck KGaA (MRK.DE), which holds a standard of care position. Keytruda's trial can be seen as a direct challenge to this established market. If Keytruda succeeds in the trial and obtains PMDA approval, it has the potential to significantly reshape the global MCC market, which is estimated at $2 billion.
Diversification Strategy to Address the 2028 Keytruda Patent Expiration
Keytruda, Merck's top-selling drug with annual sales of $31.68 billion, faces a significant challenge with the upcoming expiration of its core substance patent in 2028. To address this, Merck is pursuing a strategy to expand its indications to include minimal residual disease (MRD), rare indications, and pediatric patients. This Japanese trial is part of a broader effort to extend the lifecycle of the original drug and defend against the entry of biosimilars after the patent expiration.
Key Indicators for Global Investors and Job Seekers
From an investor perspective, the objective response rate (ORR) and progression-free survival (PFS) data from the upcoming Phase 1/2 trial will be key determinants of the approval timeline in Japan. For those seeking employment in the biopharmaceutical industry, this trial provides a valuable case study to understand Merck's multinational clinical protocol design and local regulatory response strategies. The patient enrollment rate and initial safety profile of this trial will be indicators of the pace of Merck's oncology portfolio expansion in the Asia-Pacific region.
This KEYNOTE-G21 Phase 1/2 clinical trial represents a critical step in Merck's efforts to enter the Japanese market for Merkel Cell Carcinoma (MCC), a currently unapproved indication for Keytruda (Keytruda), which generated global sales of $31.68 billion in 2025. The global MCC treatment market is projected to grow from $1.97 billion in 2025 to up to $3.71 billion in 2035, with Pfizer's Avelumab currently holding a dominant position in Japan. From a research and clinical development perspective, this trial, which combines pediatric solid tumors and adult rare skin cancers, offers a model for efficiently generating regulatory data in rare disease areas where patient recruitment is challenging. In the medium to long term, this strategy aims to extend the market exclusivity of the original drug in Japan and mitigate potential price reductions by expanding indications to include pediatric and rare cancer patients, in anticipation of the Keytruda patent expiration in 2028. Investors should closely monitor the achievement of superior objective response rates (ORR) compared to existing standard treatments and the potential for expedited review by the local regulatory agency (PMDA).
Source: ClinicalTrials.gov (api_ct)