Key Highlights
- Merck (MRK) shares experienced a nearly 4% surge in after-hours trading following positive clinical trial data.
- The OptiTROP-Lung05 Phase 3 study evaluated sac-TMT paired with Keytruda versus Keytruda monotherapy for first-line treatment of advanced non-small cell lung cancer (NSCLC).
- The dual-therapy approach demonstrated a 65% reduction in progression-free survival risk and achieved a response rate of approximately 70.2% compared to 42% with 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.
- Full trial findings will be unveiled at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting, while Chinese regulators are conducting a priority review for first-line NSCLC approval.
Merck (MRK) shares experienced a significant after-hours boost of approximately 4% following an announcement from partner Kelun-Biotech revealing that a novel drug combination significantly outperformed Keytruda monotherapy in a late-stage lung cancer clinical study.
The encouraging results stem from the OptiTROP-Lung05 Phase 3 clinical trial, which evaluated sacituzumab tirumotecan — referred to as sac-TMT — an antibody-drug conjugate, in combination with Merck’s leading oncology drug Keytruda for initial treatment of patients diagnosed with advanced non-small cell lung cancer (NSCLC).
The clinical study recruited over 400 treatment-naive patients across China who presented with advanced disease and demonstrated PD-L1 expression, a biological marker commonly used to forecast immunotherapy response potential.
The investigational combination achieved a 65% reduction in the risk of disease advancement or death when compared with Keytruda monotherapy — a statistically robust outcome. Additionally, the objective response rate reached approximately 70.2%, substantially exceeding the 42% observed among patients receiving Keytruda alone.
Overall survival metrics had not reached maturity during the September 2025 data analysis cutoff point, though Kelun-Biotech indicated positive trending in overall survival outcomes.
Understanding Sac-TMT
Sac-TMT functions as an antibody-drug conjugate — a category of precision medicine engineered to transport chemotherapy agents directly to malignant cells by attaching to a designated protein known as TROP2. This mechanism aims to maximize the cytotoxic effect at tumor sites while minimizing systemic exposure.
The therapeutic agent originated from Kelun-Biotech, a Chinese biotechnology company with Hong Kong stock exchange listing. Merck secured licensing rights for territories outside Greater China in 2022.
Sac-TMT has received approval in China for late-stage NSCLC treatment, along with additional malignancies including breast and gastrointestinal cancer types.
An application to broaden the approved indication to encompass first-line NSCLC therapy — supported by OptiTROP-Lung05 trial data — is presently undergoing priority regulatory review within China.
Tolerability and Adverse Event Profile
The combination regimen demonstrated an elevated incidence of severe adverse reactions. Approximately 55% of participants receiving the combination therapy experienced treatment-emergent adverse events classified as grade 3 or higher severity, versus roughly 31% among those receiving Keytruda monotherapy.
Frequently reported serious adverse effects encompassed neutropenia (decreased white blood cell counts) and anemia.
Approximately 4% of study participants discontinued sac-TMT and 5% discontinued Keytruda because of adverse reactions, while 5% in the Keytruda-alone cohort discontinued treatment.
Both pharmaceutical companies characterized the safety findings as aligned with established safety profiles for each individual agent.
NSCLC represents the predominant lung cancer subtype in the United States, comprising approximately 87% of all lung cancer diagnoses, per American Cancer Society data.
Comprehensive OptiTROP-Lung05 study results are scheduled for presentation during the 2026 American Society of Clinical Oncology Annual Meeting.
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