Kelun-Biotech reports strong Phase 3 data for sacituzumab tirumotecan in HR+/HER2- breast cancer

Sichuan Kelun-Biotech Biopharmaceutical Co., Ltd. (HKEX: 6990), a clinical-stage Chinese biotech company specializing in antibody-drug conjugates (ADCs), reported compelling data from its Phase 3 OptiTROP-Breast02 study evaluating sacituzumab tirumotecan (sac-TMT) in patients with previously treated hormone receptor-positive (HR+) and HER2-negative (HER2-) advanced breast cancer. The results were presented at the 2025 European Society for Medical Oncology (ESMO) Congress in Berlin by Professor Man Li of Dalian Medical University.

The trial met its primary endpoint by demonstrating a statistically significant and clinically meaningful progression-free survival (PFS) benefit. Sac-TMT achieved a median PFS of 8.3 months compared to 4.1 months with standard chemotherapy options. The hazard ratio of 0.35 indicated a 65% risk reduction in disease progression or death. The therapy also showed favorable trends in overall survival (OS), consistent benefit across HER2-zero and HER2-low subgroups, and a manageable safety profile.

The announcement marks a critical inflection point for the oncology-focused drugmaker, which is seeking regulatory approval for this new indication in China through a priority review process with the National Medical Products Administration (NMPA).

How does sacituzumab tirumotecan perform against standard chemotherapy in this patient population?

The OptiTROP-Breast02 study enrolled 399 patients with HR+/HER2- metastatic breast cancer who had already progressed on CDK4/6 inhibitors and received at least one line of chemotherapy. Patients were randomized in a 1:1 ratio to receive sac-TMT or the investigator’s choice of chemotherapy (ICC), representing typical treatment regimens used in the post-endocrine, post-CDK setting.

As of the January 22, 2025 data cut-off, sac-TMT nearly doubled median PFS to 8.3 months versus 4.1 months with chemotherapy. The treatment benefit was consistent across biomarker-defined subgroups, with HER2-zero patients showing a hazard ratio of 0.39 and HER2-low patients at 0.31, suggesting sac-TMT could deliver robust activity regardless of HER2 expression levels.

The overall response rate (ORR) and duration of response (DoR) were also superior in the sac-TMT arm. While the OS data remains immature, the trend favored sac-TMT with a hazard ratio of 0.33, pointing toward a possible survival benefit.

Safety outcomes showed that Grade 3 or higher treatment-related adverse events (TRAEs) were slightly lower for sac-TMT at 62% versus 64.8% in the ICC arm. Importantly, no patients in the sac-TMT group discontinued treatment due to TRAEs, compared to 0.5% in the chemotherapy group. Rates of pneumonitis, a key safety concern with ADCs, were low in both groups and limited to Grade 1–2 events.

Why are analysts watching Kelun-Biotech’s ADC strategy closely in 2025?

Kelun-Biotech has quietly emerged as one of China’s most advanced ADC developers. Sac-TMT is already approved for three indications in China, including triple-negative breast cancer (TNBC) and EGFR-mutant non-squamous non-small cell lung cancer (NSCLC). The company also has a major global licensing deal with Merck & Co., Inc. (known as MSD outside the U.S.), which holds exclusive commercial rights to sac-TMT outside Greater China.

This Phase 3 HR+/HER2- readout positions sac-TMT as a strong contender in one of the largest remaining ADC opportunities in breast cancer. With growing Western focus on TROP2-targeted ADCs like Gilead’s Trodelvy, Kelun’s sac-TMT appears to be positioning itself as a serious global competitor, especially in the Chinese market where local innovation is increasingly favored in reimbursement frameworks.

Institutional sentiment has been cautiously optimistic. Kelun-Biotech’s stock price has reflected this confidence, despite revenue contraction and ongoing net losses. Investors have priced in long-term upside from sac-TMT’s expanding label, especially if the HR+/HER2- indication translates into high-volume adoption.

What is the regulatory status of sacituzumab tirumotecan in China and globally?

Kelun-Biotech has submitted a new drug application (NDA) to the NMPA for sac-TMT’s use in previously treated HR+/HER2- breast cancer. This application has been accepted and is undergoing priority review. If approved, it would mark the fourth indication for sac-TMT in China, broadening its footprint in the breast cancer segment and reinforcing its positioning as the country’s most diversified TROP2 ADC franchise.

Outside China, sac-TMT is in global development via MSD, which has initiated 15 Phase 3 studies evaluating the drug across various tumor types, both as monotherapy and in combination with pembrolizumab. These studies span multiple geographies and represent the most aggressive ADC development program outside of Japan’s Daiichi Sankyo or the U.S.-based ImmunoGen.

Within China, Kelun-Biotech has launched nine registrational trials and continues to expand clinical development for sac-TMT and its broader ADC pipeline. The company’s proprietary linker technology and high drug-to-antibody ratio of 7.4 have become focal points of its differentiation strategy in the crowded ADC space.

What is Kelun-Biotech’s broader innovation strategy, and how is the pipeline progressing?

Kelun-Biotech is a holding subsidiary of Kelun Pharmaceutical Co., Ltd. (SZSE: 002422) and operates with a strong focus on biologics and novel small molecules. It has established proprietary technology platforms such as OptiDC, designed to accelerate next-generation ADC and dual-conjugate development.

The pipeline includes more than 30 innovative drug programs, with four drugs already approved in China, one in the NDA stage, and over ten in active clinical development. While oncology remains the lead focus, Kelun-Biotech is also working on assets targeting autoimmune, inflammatory, and metabolic diseases.

Its strategy hinges on dual execution: fast-track regulatory pathways in China for key oncology indications, paired with global co-development partnerships that leverage international commercialization muscle, exemplified by the MSD alliance.

How is Kelun-Biotech’s stock performing, and what does market sentiment suggest?

Kelun-Biotech’s shares (HKEX: 6990) have traded in a volatile range over the past year. The stock touched a 52-week high of HKD 581.00 but has since pulled back to the HKD 450–470 range. Analysts attribute the correction to broader sectoral pressures and the company’s significant R&D spend, which continues to impact profitability.

Despite a revenue decline of over 30% year-over-year in the first half of 2025, investor interest has remained strong due to the company’s growing clinical momentum. Institutional investors appear to be looking past short-term losses and focusing instead on the breadth of the ADC pipeline, regulatory milestones, and potential for sac-TMT to scale commercially across breast and lung cancers.

Risk factors include pricing challenges, especially in provincial Chinese markets; competition from both domestic and global ADC players; and the need to demonstrate post-approval uptake in real-world settings.

What comes next for sac-TMT and Kelun-Biotech in the ADC race?

Looking forward, industry watchers will be closely tracking the NMPA’s approval timeline for sac-TMT in HR+/HER2- breast cancer, as well as the outcome of global Phase 3 trials led by MSD. Additional key milestones include updates from Kelun-Biotech’s ongoing registrational studies, reimbursement negotiations within China’s NRDL framework, and real-world adoption metrics post-launch.

If sac-TMT succeeds in entering front-line or earlier treatment settings—especially in combination with immunotherapy—it could dramatically expand its market. Combined with Kelun-Biotech’s leadership in ADC platform development, this would further position the firm as a formidable player in the global oncology landscape.

While commercialization challenges remain, particularly in a crowded TROP2 space, sac-TMT’s robust efficacy data in multiple tumor types and manageable safety profile give it competitive viability. Investors, regulators, and patients alike will be watching closely as Kelun-Biotech moves toward what could be a franchise-defining approval.

What are the key takeaways from Kelun-Biotech’s Phase 3 data on sacituzumab tirumotecan in HR+/HER2- breast cancer?

• Sacituzumab tirumotecan (sac-TMT) achieved a median PFS of 8.3 months versus 4.1 months for chemotherapy in the Phase 3 OptiTROP-Breast02 study, demonstrating a significant 65% risk reduction in progression.

• The study showed consistent PFS benefits across HER2-low and HER2-zero subgroups, indicating the drug’s broad applicability in HR+/HER2- metastatic breast cancer regardless of HER2 expression.

• Sac-TMT also demonstrated a favorable safety profile, with fewer high-grade TRAEs leading to treatment discontinuation and low incidence of pneumonitis.

• The trial marks the first time such strong ADC data has emerged from an all-Chinese HR+/HER2- breast cancer cohort, positioning Kelun-Biotech as a leading local innovator in oncology.

• Regulatory application for this new indication has been accepted under priority review by China’s NMPA, potentially setting up sac-TMT for its fourth approved indication in the domestic market.

• Global partner Merck & Co., Inc. (MSD) is conducting 15 Phase 3 trials with sac-TMT across multiple tumor types, expanding the drug’s global footprint.

• Despite recent financial losses, Kelun-Biotech has maintained positive investor sentiment due to its robust pipeline, with sac-TMT seen as a potential flagship ADC franchise.

• Key upcoming milestones include NMPA approval for HR+/HER2- indication, reimbursement decisions in China, global trial readouts from MSD-led studies, and commercial uptake performance.