Key Highlights

  • Merck & Co. (NYSE: MRK) and Kelun-Biotech’s sac-TMT hit both primary endpoints in TroFuse-005, the first global phase 3 success for the TROP2-directed ADC
  • Overall survival improved by a statistically significant Margin versus physician’s-choice chemotherapy, with the precise hazard ratio to be disclosed at an upcoming medical meeting
  • Progression-free survival also met its primary goal, reinforcing sac-TMT’s potential as a new standard in second-line recurrent or advanced endometrial cancer
  • The trial enrolled roughly 500 patients across 15 countries, underscoring the global scope of Merck’s development strategy for the asset
  • Analysts at Leerink Partners now assign a 35% probability of sac-TMT becoming the top-selling TROP2 ADC by 2030, with peak sales estimates clustering around $2 billion

Merck & Co. (NYSE: MRK) and Kelun-Biotech’s experimental antibody–drug conjugate sacituzumab tirumotecan (sac-TMT) has become the first globally successful phase 3 therapy in endometrial cancer, a malignancy where new systemic Options remain scarce. The TroFuse-005 study met both co-primary endpoints—overall survival (OS) and progression-free survival (PFS)—according to a company release on May 21, 2026. The news immediately elevates sac-TMT into a league that includes Gilead Sciences’ Trodelvy and Daiichi Sankyo/AstraZeneca’s Datopotamab deruxtecan, both of which have carved out positions in other solid tumours and are now eyeing endometrial cancer as a fresh battleground.

The trial randomised approximately 500 patients with advanced or recurrent endometrial cancer whose disease had progressed after prior platinum-based chemotherapy. The comparator was physician’s-choice chemotherapy, a reflection of the control arm used in most gynaecologic oncology studies. Detailed hazard ratios and absolute survival gains are slated for presentation at the European Society for Medical Oncology congress in October 2026, but the companies characterised the magnitude of benefit as “clinically meaningful and statistically significant.” Such phrasing typically signals a hazard ratio comfortably below 0.70, a threshold that would place sac-TMT on par with recent breakthroughs in other tumour types.

Endometrial cancer incidence has climbed steadily in developed markets—partly due to rising obesity and aging populations—and five-year survival for advanced disease hovers around 17% according to the American Cancer Society. The lack of biomarker-driven options has left oncologists reliant on sequential chemotherapy and, more recently, immunotherapy combinations. Sac-TMT targets TROP2, a cell-surface protein overexpressed in roughly 80% of endometrial tumours, a prevalence profile that mirrors breast and urothelial cancers. Merck licensed the ADC from Kelun-Biotech in 2021 under a deal that included up to $1.4 billion in milestones, underscoring the asset’s strategic importance to both partners.

Why this trial matters for Merck’s oncology pipeline

For Merck (NYSE: MRK), sac-TMT represents one of the most advanced externally sourced oncology Assets in its late-stage pipeline. The company’s internal pipeline—anchored by Keytruda (pembrolizumab)—has delivered blockbuster revenues but is facing growing biosimilar competition in several indications. Sac-TMT gives Merck a product that can be positioned as a precision oncology play, particularly in TROP2-high tumours where competition is intensifying. Analysts at Evercore ISI estimate peak global sales of $1.8–2.3 billion for sac-TMT, assuming label expansion into triple-negative breast cancer and non-small-cell lung cancer—two indications already under investigation. The TroFuse-005 win also validates Merck’s partnering strategy, which has leaned heavily on Chinese biotechs for novel ADCs; Kelun-Biotech’s Manufacturing and regulatory expertise in Asia could accelerate global Supply once approval is secured.

Whilst Merck’s own Keytruda Franchise still generates more than $25 billion in annual Revenue, the group has been methodically diversifying its oncology portfolio beyond PD-1 monotherapy. Sac-TMT’s success contrasts with recent setbacks—most notably the 2025 termination of the Phase 3 LEAP-005 trial in colorectal cancer—highlighting the inherent risk in external asset licensing. Yet the endometrial data suggest that Merck’s diligence in target selection—TROP2’s relatively restricted expression in normal tissue—has paid off. The company plans to file for Accelerated Approval in the United States by mid-2027, a timeline that would position sac-TMT for a potential 2028 launch, assuming no major regulatory hurdles.

Kelun-Biotech’s breakout moment in the global ADC race

For Kelun-Biotech, a Chengdu-based biotech with a Market Capitalisation of approximately $8 billion, sac-TMT’s phase 3 triumph is transformative. Prior to this trial, Kelun had secured approvals only in China—most notably for its own TROP2 ADC, disitamab vedotin (Aidixi)—and had yet to notch a global phase 3 win. The TroFuse-005 collaboration with Merck provides Kelun with global development, regulatory, and commercial infrastructure that would be difficult to replicate independently. Industry watchers note that Kelun’s process chemistry—optimised for high drug-to-antibody ratio and stability—may have contributed to the favourable therapeutic index observed in the trial.

The deal Economics are also favourable to Kelun. Merck is responsible for global manufacturing and commercialisation, while Kelun retains rights in China—its home market—and is eligible for up to $1.4 billion in milestones, plus double-digit royalties on ex-China net sales. Analysts at Bernstein estimate that ex-China royalties could reach mid-teens by 2030, implying a potential $200–300 million annual revenue stream for Kelun from sac-TMT alone. The success also burnishes Kelun’s reputation among Western partners, a critical asset as it seeks to in-license additional ADCs for global development.

Yet the Partnership is not without risk. Kelun’s manufacturing footprint is still largely Asia-centric, and supply chain bottlenecks—particularly for cytotoxins like SN-38—could constrain commercial launch timelines. Moreover, competition in the TROP2 space is fierce; Gilead’s Trodelvy (sacituzumab govitecan) already holds accelerated approval in triple-negative breast cancer, and Daiichi Sankyo/AstraZeneca’s Datopotamab deruxtecan is advancing rapidly in lung and breast indications. Kelun and Merck will need to differentiate sac-TMT on safety profile, dosing convenience, and cost—factors that could influence payer decisions in both the US and Europe.

Investor sentiment: short-term relief, long-term questions

Investors greeted the news with muted enthusiasm. Merck’s shares closed essentially flat on the day, reflecting the market’s expectation that sac-TMT’s contribution to overall revenue—even at peak—would be modest relative to Keytruda. The company’s oncology pipeline remains dominated by Keytruda, which accounts for roughly one-third of total group revenue. Analysts at UBS calculate that sac-TMT could add $0.15–0.20 to Merck’s 2030 Earnings Per Share, a figure that pales beside the $1.50–2.00 contribution from Keytruda biosimilar-resistant indications.

For Kelun-Biotech, the stock reaction was more pronounced. Shares surged 14% in Hong Kong trading on May 22, 2026, adding roughly $1.1 billion to its market capitalisation. The move underscores the Scarcity value of global phase 3 data for Chinese biotechs, particularly in oncology where late-stage failures are common. Yet the rally also raises questions about sustainability. Kelun’s pipeline is heavily concentrated in ADCs, and any setback in subsequent indications—such as non-small-cell lung cancer or urothelial carcinoma—could trigger a sharp re-rating. Moreover, the broader Chinese biotech sector remains under pressure from geopolitical tensions and pricing pressures in the US market.

The TroFuse-005 data also reverberate through the broader ADC ecosystem. Trodelvy’s manufacturer, Gilead Sciences (Nasdaq: GILD), has already filed for a label expansion in hormone receptor-positive breast cancer, and its shares dipped 2% on the news as investors reassessed competitive intensity. Daiichi Sankyo (TSE: 4568), meanwhile, is advancing Datopotamab deruxtecan in multiple tumour types, including endometrial cancer, with interim data expected in late 2026. The endorsement of TROP2 as a viable target in endometrial cancer—historically a niche indication for ADCs—could catalyse additional Investment in the space, particularly for next-generation linkers and payloads designed to mitigate toxicity.

Regulatory and payer dynamics: what comes next

The most immediate hurdle is regulatory. Merck plans to file for accelerated approval in the US based on the TroFuse-005 data, a pathway that typically requires a single pivotal trial demonstrating substantial improvement over available therapy. The FDA’s Oncologic Drugs Advisory Committee is likely to scrutinise the dataset closely, particularly given the absence of a biomarker-driven selection strategy in the trial. Analysts at SVB Securities note that the agency’s recent crackdown on accelerated approvals in oncology—exemplified by the 2024 Withdrawal of Roche’s Tecentriq in triple-negative breast cancer—could prolong the review timeline.

Payer acceptance will hinge on cost-effectiveness. The wholesale Acquisition cost of Trodelvy in the US is approximately $15,000 per month, a figure that has drawn scrutiny from the Institute for Clinical and Economic Review. Kelun’s manufacturing advantage in China—where cytotoxic payloads are produced at lower cost—could allow sac-TMT to price competitively, particularly in emerging markets. Yet in the US, where endometrial cancer is more prevalent among older, Medicare-eligible patients, formulary Placement and patient access programmes will be critical. Merck’s experience with Keytruda’s broad reimbursement in oncology should ease some concerns, but the ADC market is far more price-sensitive.

Globally, the data could accelerate regional approvals. Europe’s EMA typically follows FDA decisions with a lag of 6–12 months, while China’s National Medical Products Administration—where Kelun already markets Aidixi—may grant a supplementary approval based on the global data. The trial’s multicountry design, which included sites in the US, Europe, and Asia, should satisfy regional regulators’ demands for geographic diversity.