Merck’s TROP2 ADC, Licensed from Kelun-Biotech, Achieves Milestone in First Global Phase III Trial

Merck (MSD) announced positive topline results from a global Phase III clinical trial evaluating Sacituzumab Tirumotecan (Sac-TMT; R&D code: MK-2870/SKB264), a TROP2-targeted antibody-drug conjugate (ADC) licensed from Kelun-Biotech, in patients with endometrial cancer.

This success marks the first reported result among 17 late-stage clinical studies currently underway for this molecule. In the shadow of the looming "patent cliff" for the blockbuster immunotherapy Keytruda (pembrolizumab), the success of Sac-TMT represents not only a clinical victory but also a critical pillar in Merck's strategic ambition to reach $70 billion in annual sales by the next decade.

Clinical Data Analysis: A Breakthrough in the Post-IO Era of Endometrial Cancer

The successful global Phase III trial focused on patients with endometrial cancer who had progressed following standard platinum-based chemotherapy and immune checkpoint inhibitor (IO) therapy (e.g., Keytruda).

• Primary Endpoints: In a pre-specified interim analysis, Sac-TMT demonstrated a statistically significant and clinically meaningful improvement in both Overall Survival (OS) and Progression-Free Survival (PFS)compared to physician-chosen chemotherapy (control arm).

• Response Rates: Merck highlighted that the Sac-TMT arm exhibited a superior Objective Response Rate (ORR).

• Safety: The safety profile remained consistent with earlier testing, with no new safety signals observed. This stability is vital for the application of ADC therapies in heavily pre-treated, multi-line settings.

R&D Perspective: For patients whose endometrial cancer has progressed following platinum and IO therapy, clinical options remain severely limited. The efficacy demonstrated by Sac-TMT in this "post-IO/platinum" setting validates its potential as a potent second/third-line therapy and underscores the high value of TROP2 expression as a therapeutic target in this malignancy.

The TROP2 ADC Landscape: The Differentiated Edge of Sac-TMT

Competition in the TROP2 ADC arena is intensifying. Sac-TMT faces direct competition from Gilead’s Trodelvy(approved) and AstraZeneca/Daiichi Sankyo’s Dato-DXd (under regulatory review).

Sac-TMT distinguishes itself through its unique molecular design:

1. Novel Linker and Payload: Sac-TMT utilizes a proprietary non-cleavable linker conjugated to a novel topoisomerase I inhibitor payload.

2. Optimized DAR: Through an optimized Drug-to-Antibody Ratio (DAR), Sac-TMT achieves high-efficiency delivery within tumor tissues while balancing systemic toxicity.

3. Clinical Validation: Beyond this endometrial cancer trial, clinical data for non-small cell lung cancer (NSCLC) conducted by Kelun in China has been accepted by the NMPA, with further details to be presented at the ASCO annual meeting later this month. Analysts anticipate that its validation in lung cancer will further solidify its "best-in-class" potential.

Merck’s Strategic Ambition: Filling the "Power Vacuum" Post-Keytruda

Merck leadership has repeatedly emphasized that no single medicine can fully replicate the footprint of Keytruda, necessitating a "combination punch" strategy. Sac-TMT is a key heavy-hitter in this arsenal.

• Pipeline Density: Merck has initiated development plans for Sac-TMT across 17 different tumor types, including major cancers such as lung, breast, and gastric cancer.

• Global Partnership Paradigm: Sac-TMT is the core of a wide-ranging alliance between Merck and Kelun, involving $950 million in upfront payments and billions in potential milestone payments. This success significantly bolsters the confidence of Multinational Corporations (MNCs) in China-origin innovation pipelines.

• Commercial Outlook: Capital markets are highly optimistic about the molecule's prospects. RBC Capital Markets analyst Trung Huynh projects that Sac-TMT could generate $2.6 billion in annual sales by 2030, surging to $7.2 billion by 2034.

Summary and Outlook

The success of Sac-TMT in the global Phase III endometrial cancer study marks a new stage for TROP2-targeted therapy. For drug development professionals, the following developments are critical to monitor:

1. ASCO 2026: Disclosure of detailed clinical data for Sac-TMT in the NSCLC setting.

2. Breast Cancer Strategy: Progress in global head-to-head studies targeting TNBC (Triple-Negative Breast Cancer) and HR+/HER2- breast cancer.

3. Combination Therapy: Explorations of Sac-TMT in combination with Keytruda for first-line treatment.

With this initial "opening win," Merck is accelerating the commercialization of its ADC portfolio. Amidst the global ADC development frenzy, whether Sac-TMT can leverage its robust performance across multiple refractory solid tumors to achieve market leadership remains a key narrative to watch.