Key Highlights
- Merck (MRK) stock surged approximately 4% during after-hours sessions after promising clinical trial data was released.
- The OptiTROP-Lung05 Phase 3 study evaluated sac-TMT paired with Keytruda versus Keytruda monotherapy as initial treatment for advanced non-small cell lung cancer (NSCLC) patients.
- The therapy combination demonstrated a 65% reduction in disease progression or death risk, with response rates reaching approximately 70.2% compared to just 42% for Keytruda monotherapy.
- Sac-TMT represents an antibody-drug conjugate (ADC) that targets TROP2, originally developed by Kelun-Biotech of China and licensed to Merck in 2022.
- Complete study findings will be shared at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting, while Chinese regulators currently review the drug for expanded first-line NSCLC approval under priority status.
Merck (MRK) stock experienced a substantial after-hours rally of nearly 4% following Kelun-Biotech’s announcement that a novel drug pairing significantly outperformed Keytruda monotherapy in advanced-stage lung cancer patients.
The encouraging results originate from the OptiTROP-Lung05 Phase 3 clinical study, which evaluated sacituzumab tirumotecan—commonly referred to as sac-TMT—an antibody-drug conjugate administered alongside Merck’s blockbuster oncology treatment Keytruda for first-line therapy in patients diagnosed with advanced non-small cell lung cancer (NSCLC).
Researchers enrolled over 400 treatment-naive patients across China who presented with advanced-stage disease and exhibited PD-L1 expression, a biological marker that helps predict immunotherapy treatment response.
The dual-therapy approach reduced the risk of cancer progression or patient death by 65% when compared to Keytruda monotherapy—representing statistically significant and clinically meaningful results. Additionally, the objective response rate reached approximately 70.2%, substantially higher than the 42% observed among patients receiving Keytruda alone.
Overall survival metrics had not yet reached statistical maturity at the September 2025 data cutoff point, though Kelun-Biotech indicated encouraging trends pointing toward survival benefits.
Understanding Sac-TMT Technology
Sac-TMT belongs to the antibody-drug conjugate category—a sophisticated class of targeted cancer therapies engineered to deliver chemotherapy agents directly to malignant cells by attaching to a specific surface protein known as TROP2. This approach aims to concentrate the cytotoxic payload at tumor sites while minimizing systemic exposure and reducing collateral damage to healthy tissues.
The therapeutic agent was originally discovered and developed by Kelun-Biotech, a Chinese biotechnology company traded on the Hong Kong stock exchange. Merck secured licensing rights for territories outside Greater China through a 2022 agreement.
Chinese health authorities have already granted sac-TMT approval as a late-stage treatment option for NSCLC patients, along with approvals for breast cancer and gastrointestinal malignancies.
Regulatory submission for expanded labeling covering first-line NSCLC treatment—supported by the OptiTROP-Lung05 trial data—is currently undergoing priority review by Chinese regulatory agencies.
Adverse Events and Safety Considerations
The combination regimen demonstrated an elevated incidence of serious adverse reactions. Approximately 55% of participants receiving the combination therapy experienced treatment-related adverse events classified as grade 3 or higher severity, compared to roughly 31% among those receiving Keytruda monotherapy.
Frequently reported serious complications included neutropenia (low white blood cell counts) and anemia.
Approximately 4% of study participants discontinued sac-TMT treatment and 5% discontinued Keytruda administration due to adverse reactions, compared with 5% discontinuation rates in the single-agent Keytruda control arm.
Both companies characterized the safety profile as generally consistent with the established toxicity profiles of each individual agent.
Non-small cell lung cancer represents the predominant histological subtype of lung cancer diagnosed in the United States, comprising approximately 87% of all lung cancer cases based on American Cancer Society statistics.
Complete findings from the OptiTROP-Lung05 study are scheduled for presentation during the 2026 American Society of Clinical Oncology Annual Meeting.
