Sichuan Kelun-Biotech Biopharmaceutical Co. (HKEx: 6990.HK) announced that its TROP2-directed antibody-drug conjugate (ADC) sacituzumab tirumotecan met the primary endpoint of progression-free survival in a Phase III trial for first-line advanced triple-negative breast cancer. The result positions the drug candidate for a potential regulatory filing in China and adds to a growing body of evidence for the ADC class in a disease where treatment options remain constrained.
The OptiTROP-Breast03 trial is a randomized, open-label, multicenter Phase III study evaluating sac-TMT monotherapy against investigator's choice of chemotherapy in patients with unresectable locally recurrent or metastatic TNBC who had not received prior systemic therapy for advanced disease. The enrolled population includes both PD-L1-negative patients and PD-L1-positive patients who relapsed after prior anti-PD-(L)1 therapy in early-stage disease — two subgroups for whom current approved options are limited.
At a prespecified interim analysis, the Independent Data Monitoring Committee concluded that sac-TMT demonstrated a statistically significant and clinically meaningful improvement in PFS progression-free survival breast cancer endpoint versus chemotherapy. The company described the improvement as meeting both the statistical and clinical thresholds, though specific numerical data — median PFS, hazard ratio, and confidence intervals — were not disclosed in the announcement. Overall survival data remain immature at this stage, with the company noting a positive directional trend; follow-up will continue per protocol with OS to be evaluated at subsequent prespecified analyses. The safety profile was consistent with prior studies, and no new safety signals were identified.
Full data are expected to be presented at a future medical conference. Nevertheless, the IDMC's conclusion that both statistical significance and clinical meaningfulness were achieved carries weight, particularly given the trial's focus on a patient population that includes those ineligible for or refractory to checkpoint inhibition.
Sacituzumab tirumotecan TNBC development context
Sac-TMT is a next-generation TROP2-directed ADC in which the anti-TROP2 antibody sacituzumab is conjugated to a topoisomerase I inhibitor via a bifunctional linker with a drug-to-antibody ratio of 7.4. The construct is designed to release the payload intracellularly and can act on adjacent tumor cells through a bystander effect. This mechanistic profile distinguishes sac-TMT from the first-generation TROP2 ADC in the class, Gilead Sciences' Trodelvy (sacituzumab govitecan), which uses a different payload and carries a lower drug-to-antibody ratio.
The Kelun-Biotech Phase III trial result in first-line TNBC builds on the drug's existing approval in China for the second-line-plus setting, which was granted based on the OptiTROP-Breast01 study in patients who had received at least two prior systemic therapies. OptiTROP-Breast03 represents the first registrational Phase III study of sac-TMT to achieve a positive result in the first-line TNBC setting, extending the drug's potential clinical utility to an earlier and larger patient population.
Kelun-Biotech licensed exclusive rights to develop, manufacture, and commercialize sac-TMT outside Greater China to Merck & Co. in May 2022, under which the drug is also known as MK-2870. MSD has since initiated 17 ongoing global Phase III studies of the molecule as monotherapy or in combination with Merck's Keytruda (pembrolizumab) across multiple tumor types. Merck is also assessing sac-TMT in TNBC in the ongoing global Phase III TroFuse-011 study (NCT06841354).
Where sac-TMT fits in first-line TNBC landscape
The first-line metastatic TNBC setting is defined by a narrow set of approved options and a substantial unmet need in biomarker-unselected patients. Merck's Keytruda combined with chemotherapy is the established standard of care for patients with PD-L1 CPS ≥10, based on the KEYNOTE-355 data, but this biomarker restriction excludes approximately 60% of patients with metastatic TNBC who are PD-L1-negative. For those patients, and for patients who relapsed on prior checkpoint inhibitor therapy in the early-stage setting, the first-line standard of care remains cytotoxic chemotherapy alone.