Merck (MRK) Stock Surges on Breakthrough Lung Cancer Combination Therapy Results

TLDR

• Merck (MRK) shares jumped approximately 4% during after-hours trading after positive trial data was released.
• The OptiTROP-Lung05 Phase 3 study evaluated sac-TMT plus Keytruda versus Keytruda monotherapy in first-line advanced non-small cell lung cancer (NSCLC) patients.
• The drug combination reduced progression or death risk by 65% and achieved approximately 70.2% response rate compared to 42% with Keytruda monotherapy.
• Sac-TMT represents an antibody-drug conjugate (ADC) that targets TROP2, created by Kelun-Biotech in China and licensed to Merck in 2022.
• The complete data will be shared at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting, while China conducts priority review for first-line NSCLC approval.

Merck (MRK) shares experienced a nearly 4% surge in after-hours trading following partner Kelun-Biotech’s announcement that a novel drug combination demonstrated superior efficacy compared to Keytruda monotherapy in late-stage lung cancer research.

Merck & Co., Inc., MRK

The results originate from the OptiTROP-Lung05 Phase 3 clinical study, evaluating sacituzumab tirumotecan — referred to as sac-TMT — an antibody-drug conjugate administered alongside Merck’s leading oncology treatment Keytruda for first-line therapy in patients diagnosed with advanced non-small cell lung cancer (NSCLC).

The study recruited over 400 treatment-naive patients in China presenting with advanced disease and PD-L1 expression, a biological marker utilized to forecast immunotherapy effectiveness.

The combination therapy demonstrated a 65% reduction in disease progression or mortality risk when compared to Keytruda monotherapy — representing a statistically significant outcome. Additionally, the response rate reached approximately 70.2%, contrasting with 42% among patients receiving Keytruda alone.

Overall survival data remained immature during the September 2025 analysis checkpoint, though Kelun-Biotech identified a promising trend in this metric.

What Is Sac-TMT?

Sac-TMT belongs to the antibody-drug conjugate category — a targeted therapeutic class engineered to transport chemotherapy agents directly to malignant cells through binding to a designated protein known as TROP2. This approach aims to concentrate the cytotoxic component at the tumor site while minimizing systemic exposure.

The therapy was developed by Kelun-Biotech, a Chinese biotechnology company with Hong Kong Stock Exchange listing. Merck obtained licensing rights for territories outside Greater China in 2022.

Sac-TMT has received approval in China for late-line NSCLC treatment, along with additional malignancies including breast and gastrointestinal cancers.

An application to broaden its indication to encompass first-line NSCLC — supported by OptiTROP-Lung05 findings — is presently undergoing priority review by Chinese regulatory authorities.

Safety and Side Effects

The combination regimen exhibited an elevated incidence of severe adverse events. Approximately 55% of patients receiving the combination experienced treatment-emergent adverse events of grade 3 or higher, versus roughly 31% in the Keytruda monotherapy cohort.

Prevalent serious adverse reactions comprised decreased white blood cell counts and anemia.

Approximately 4% of patients discontinued sac-TMT and 5% stopped Keytruda because of adverse effects, compared with 5% in the monotherapy arm.

Both companies characterized the safety profile as aligned with established profiles of each medication.

NSCLC represents the predominant lung cancer subtype in the United States, comprising approximately 87% of all diagnoses, per the American Cancer Society.

Complete OptiTROP-Lung05 findings are scheduled for presentation during the 2026 American Society of Clinical Oncology Annual Meeting.

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