Key Highlights
- Merck (MRK) shares surged approximately 4% during after-hours trading on the heels of positive clinical trial data.
- The late-stage OptiTROP-Lung05 study evaluated sac-TMT paired with Keytruda versus Keytruda monotherapy for initial treatment of advanced non-small cell lung cancer (NSCLC).
- The dual-drug regimen demonstrated a 65% reduction in progression or mortality risk and achieved an approximate 70.2% response rate compared to 42% with Keytruda monotherapy.
- Sac-TMT represents an antibody-drug conjugate (ADC) that targets TROP2, originally created by Kelun-Biotech of China and licensed to Merck in 2022.
- The findings will be unveiled at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting, while China is currently conducting priority review for the therapy’s label expansion as first-line NSCLC treatment.
Merck (MRK) shares experienced a nearly 4% surge in after-hours market activity following partner Kelun-Biotech’s announcement that a novel therapeutic combination demonstrated superior efficacy compared to Keytruda monotherapy in an advanced-stage lung cancer clinical trial.
The positive results emerged from the Phase 3 OptiTROP-Lung05 clinical study, which evaluated sacituzumab tirumotecan — referred to as sac-TMT — an antibody-drug conjugate, in combination with Merck’s leading oncology asset Keytruda for initial treatment of patients diagnosed with advanced non-small cell lung cancer (NSCLC).
The clinical investigation enrolled over 400 treatment-naïve Chinese patients presenting with advanced-stage disease and expressing PD-L1, a biological marker utilized to forecast immunotherapy responsiveness.
The combination regimen reduced the risk of disease advancement or mortality by 65% when compared with Keytruda monotherapy — representing a statistically robust outcome. Additionally, the objective response rate reached approximately 70.2%, contrasting with 42% among patients receiving Keytruda exclusively.
Overall survival information had not reached maturity during the September 2025 data analysis cutoff date, though Kelun-Biotech observed an encouraging trend regarding this endpoint.
Understanding Sac-TMT
Sac-TMT belongs to the antibody-drug conjugate category — a therapeutic class engineered to transport chemotherapy agents specifically to malignant cells through binding to a designated protein known as TROP2. This approach aims to focus the cytotoxic agent at tumor sites while minimizing systemic exposure.
The therapy was developed by Kelun-Biotech, a Chinese biotechnology company with Hong Kong stock exchange listing. [[LINK_START_2]]Merck[[LINK_END_2]] secured licensing rights for territories outside Greater China during 2022.
Chinese regulatory authorities have already granted sac-TMT approval as a subsequent-line therapy for NSCLC, along with additional malignancies encompassing breast and gastrointestinal tumors.
An application seeking label expansion to encompass first-line NSCLC treatment — supported by OptiTROP-Lung05 findings — is presently undergoing priority regulatory assessment in China.
Tolerability and Adverse Reactions
The combination therapy was associated with elevated rates of significant adverse effects. Approximately 55% of subjects receiving the combination experienced treatment-related adverse events classified as grade 3 or higher severity, versus roughly 31% among the Keytruda monotherapy cohort.
Frequently observed severe reactions encompassed neutropenia and anemia.
Approximately 4% of participants discontinued sac-TMT while 5% halted Keytruda treatment owing to tolerability issues, compared with 5% discontinuation in the Keytruda-only group.
Both companies characterized the safety profile as aligned with established knowledge regarding each individual agent.
NSCLC represents the predominant lung cancer subtype in the United States, comprising approximately 87% of total diagnoses, per American Cancer Society statistics.
Complete OptiTROP-Lung05 study results are scheduled for presentation during the 2026 American Society of Clinical Oncology Annual Meeting.
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