The ADC That Beat Keytruda: What Merck and Kelun's NSCLC Data Mean for the Future of Lung Cancer Treatment

For more than a decade, pembrolizumab has been the immovable object at the center of first-line non-small cell lung cancer treatment. Keytruda, Merck's blockbuster PD-1 inhibitor, became the default standard of care for PD-L1-positive NSCLC patients not harboring targetable mutations, generating billions in annual revenue and reshaping how oncologists approach the disease. The question the field has been asking ever since is not whether Keytruda works, but what it would take to beat it. On May 21, 2026, an answer arrived from an unexpected direction.

Data released ahead of the 2026 American Society of Clinical Oncology annual meeting showed that combining sacituzumab tirumotecan, a TROP2-directed antibody-drug conjugate developed by Kelun-Biotech and licensed to Merck, with pembrolizumab itself reduced the risk of disease progression or death by 65 percent compared to pembrolizumab monotherapy in treatment-naive, PD-L1-positive advanced NSCLC. The p-value was below 0.0001. The overall response rate in the combination arm reached 70.2 percent, against 42 percent for Keytruda alone. These are not incremental numbers. They represent the first randomized Phase 3 win for an ADC-checkpoint inhibitor combination in the frontline NSCLC setting, and they arrive at a moment when the competitive landscape for this indication is shifting faster than at any point in the past decade.

What the OptiTROP-Lung05 Data Actually Show

The trial, conducted in China and led by Kelun-Biotech, enrolled treatment-naive patients with PD-L1-positive advanced NSCLC and randomized them to receive either sacituzumab tirumotecan plus pembrolizumab or pembrolizumab alone. At a median follow-up of 10.5 months, the median progression-free survival in the combination arm had not yet been reached, compared to 5.7 months for pembrolizumab monotherapy. That is a striking gap. The hazard ratio and the depth of the PFS improvement both suggest a treatment effect that goes well beyond what the field has seen from adding a second checkpoint inhibitor to PD-1 blockade.

The benefit appeared consistent across subgroups. In PD-L1-low patients, defined as a tumor proportion score below 50 percent, the combination reduced progression risk by 72 percent. In PD-L1-high patients, the reduction was 53 percent. The drug worked across both squamous and nonsquamous histologies, with hazard ratios of 0.44 and 0.28 respectively. That breadth matters commercially and clinically, because it suggests the combination's benefit is not confined to a narrow biomarker-selected population.

Overall survival data were not mature at the September 2025 data cutoff, but a preliminary 45 percent improvement in favor of the combination arm was observed. OS is the endpoint that ultimately drives regulatory decisions and clinical adoption in first-line NSCLC, and the immature but directionally strong signal will be watched closely as the trial matures.

On safety, grade 3 or higher treatment-emergent adverse events occurred in 55.3 percent of patients in the combination arm versus 31.4 percent in the monotherapy group. The discontinuation rate for sacituzumab tirumotecan was 3.8 percent. These numbers reflect the added toxicity burden of combining an ADC with immunotherapy, and they will require careful consideration as the regimen moves toward potential regulatory review. The investigators described the profile as generally manageable, and the discontinuation rate for the ADC component was low.

The Competitive Context That Makes This Data Set Consequential

To understand why this result matters beyond the trial itself, it helps to situate it within the broader competitive dynamics now reshaping first-line NSCLC. The field is currently watching two distinct drug classes compete for the right to displace pembrolizumab monotherapy as the standard of care: PD-1 by VEGF bispecific antibodies and TROP2-directed ADCs combined with checkpoint inhibitors.

The bispecific antibody ivonescimab, developed by Akeso and partnered with Summit Therapeutics, generated significant attention after the Harmoni-2 trial showed a 49 percent improvement in PFS versus Keytruda alone in the same first-line, PD-L1-positive NSCLC population in Chinese patients. That result was considered a landmark. The OptiTROP-Lung05 data, with a 65 percent PFS improvement and a longer follow-up period, appear to show a larger effect size in a comparable population, though cross-trial comparisons carry inherent limitations given differences in patient selection and trial design.

The comparison is not merely academic. Both drugs are being developed for global markets, and the question of which approach, ADC-plus-checkpoint or bispecific antibody, delivers superior outcomes in this setting will shape prescribing patterns, regulatory submissions, and commercial positioning for years. The OptiTROP-Lung05 data give the ADC approach its strongest argument yet.

What Sacituzumab Tirumotecan Is and Why It Is Different

Sacituzumab tirumotecan is a TROP2-directed ADC with a belotecan-derived topoisomerase I inhibitor payload and a bifunctional linker designed to maximize payload delivery to tumor cells while minimizing systemic payload loss. TROP2 is overexpressed on tumor cells in many common cancers, including approximately 70 percent of NSCLC cases, making it an attractive target for ADC-based approaches. What distinguishes sac-TMT from other TROP2 ADCs, including AstraZeneca and Daiichi Sankyo's Datroway, is the design of both ends of the linker, a feature Merck has highlighted as central to the drug's pharmacological profile.

Merck has made an unusually deep commitment to this asset. The company is running 17 global Phase 3 trials across multiple tumor types through its TroFuse development program, spanning more than 15,000 patients worldwide. The first global trial to read out positive was TroFuse-005, which met both PFS and OS endpoints in previously treated endometrial cancer. The OptiTROP-Lung05 result, while conducted in China, adds a second major Phase 3 win and establishes the combination's potential in the most commercially significant NSCLC setting.

Merck also holds a Commissioner's National Priority Voucher from the FDA to expedite future regulatory review of sac-TMT, a signal of the agency's recognition of the drug's potential strategic importance. That voucher could meaningfully accelerate the timeline to a US regulatory submission once global data from TroFuse-007, which is evaluating the combination in PD-L1-high patients globally, become available.

The Broader Implications for Oncology Drug Development

The OptiTROP-Lung05 result is a data point in a larger story about how the oncology field is evolving beyond the checkpoint inhibitor paradigm. PD-1 and PD-L1 inhibitors transformed cancer treatment, but their limitations are well understood. A meaningful proportion of patients do not respond, and among those who do, durable responses are not guaranteed. The field has been searching for combination strategies that can extend the benefit of checkpoint blockade to more patients and produce deeper, more durable responses.

ADCs represent one of the most promising answers to that search. By delivering cytotoxic payloads directly to tumor cells expressing a target antigen, they can kill cancer cells through a mechanism that is orthogonal to immune checkpoint modulation. When combined with a checkpoint inhibitor, the hypothesis is that ADC-mediated tumor cell death releases antigens that prime the immune response, creating a synergy that neither agent achieves alone. The OptiTROP-Lung05 data, with a 70 percent overall response rate, are consistent with that hypothesis playing out in a clinical setting.

For the roughly 250,000 Americans diagnosed with NSCLC each year, the majority of whom present with advanced disease, the development of a combination regimen that substantially outperforms the current standard of care in PD-L1-positive patients would represent a meaningful clinical advance. The full data from OptiTROP-Lung05 will be presented at ASCO 2026 in Chicago later this month, and the field will be watching closely for the subgroup analyses, the OS trajectory, and the safety details that will determine whether this result translates into a regulatory submission and, ultimately, a new standard of care.

The immovable object at the center of first-line NSCLC treatment may not be as immovable as it once appeared. What comes next will depend on whether the OS data mature in the same direction as the PFS signal, and whether the global TroFuse-007 trial can replicate the effect in a broader population. But the direction of travel is now clear, and it points toward a future in which the question is not whether to add an ADC to checkpoint blockade in lung cancer, but which ADC, in which patients, and at what cost.