Sac-TMT Meets PFS Endpoint in Advanced TNBC Amid New Biomarker Research

Sacituzumab tirumotecan (sac-TMT) met its primary end point of progression-free survival (PFS) as a first-line treatment for patients with unresectable locally recurrent or metastatic triple-negative breast cancer (TNBC), according to a prespecified interim analysis of the phase 3 OptiTROP-Breast03 trial. An Independent Data Monitoring Committee concluded that sac-TMT monotherapy demonstrated a statistically significant and clinically meaningful improvement in PFS compared with investigator's choice of chemotherapy; overall survival data remain immature, though a positive trend was observed.

OptiTROP-Breast03 is a randomized, open-label, multicenter phase 3 clinical study designed to evaluate the efficacy and safety of sac-TMT vs investigator's choice of chemotherapy in patients with unresectable recurrent or metastatic TNBC who have not received prior systemic therapy for advanced disease. The trial enrolled two patient populations with limited existing treatment options: those with PD-L1-negative expression and those with PD-L1-positive expression who relapsed after prior anti-PD-(L)1 inhibitor therapy in the early-stage setting. The two independent primary end points are PFS and overall survival. The safety profile was consistent with that seen in prior studies, with no new signals identified. This result marks the first registrational phase 3 study of sac-TMT to demonstrate a positive outcome in the first-line TNBC setting. Based on these results, the company plans to engage with the Center for Drug Evaluation of China's National Medical Products Administration to discuss the regulatory pathway for sac-TMT in this indication. The global phase 3 TroFuse-011 trial, evaluating sac-TMT alone or in combination with pembrolizumab as first-line treatment for patients with PD-L1 combined positive score of less than 10, remains ongoing.

Sac-TMT is a novel anti-TROP2 human antibody-drug conjugate developed with a bifunctional linker that connects the anti-TROP2 monoclonal antibody sacituzumab irreversibly to a belotecan-derivative topoisomerase I inhibitor payload. The construct carries a drug-to-antibody ratio of 7.4. Upon binding to TROP2 on tumor cell surfaces, sac-TMT is endocytosed and releases its payload intracellularly, inducing DNA damage, cell-cycle arrest, and apoptosis. The membrane-permeable payload KL610023 also enables a bystander effect, allowing cytotoxic activity in adjacent tumor cells.

In a study published in npj Precision Oncology, a multi-center real-world cohort study revealed that HER2-low TNBC patients had poorer responses to immunotherapy than HER2-0 patients, whereas no significant difference was observed with chemotherapy alone; these findings were validated in independent prospective cohorts (ISPY-2 and NeoTRIP). Single-cell multi-omics demonstrated that HER2-low tumors exhibited reduced expression of major histocompatibility complex and immune checkpoint molecules, along with diminished T-cell activity, relative to HER2-0 tumors. Following immunotherapy, HER2-low tumors showed no significant downregulation of targeted immune checkpoint molecules and less pronounced T-cell clonal remodeling. These findings establish HER2-low expression as a negative predictor of immunotherapy response, shaped by a less immunogenic tumor microenvironment.

Researchers at The University of Texas MD Anderson Cancer Center introduced a biomarker named TmS (tumor mRNA signature), which accounts not only for the ratio of tumor cells to stromal and immune cells but also adjusts for cancer-specific aneuploidy, thereby normalizing gene expression levels more accurately against chromosomal variation. Tested on a multi-ethnic cohort of 575 TNBC patients spanning diverse Western and Asian populations, TmS stratified patients into distinct prognostic groups: high TmS represented a better prognosis and more favorable response to chemotherapy, while low TmS indicated poorer clinical outcomes. This stratification outperformed prevailing predictive methodologies. Comparative analyses between Western and Asian patient cohorts revealed variations in the tumor microenvironment that may influence therapeutic responsiveness. Researchers previously cataloged and evaluated 43 extant deconvolution methods, noting limitations in their ability to capture gene expression shifts driven by microenvironmental factors.

A study published in PLoS One developed TNBC prognosis predictive models with a predictive performance exceeding 0.94, whereas no prior study had demonstrated a model with predictive performance exceeding 0.85. Applying nine selected markers to five independent datasets demonstrated their potential as TNBC-specific prognostic markers. Most of these genes, including GPR61, PZP, IGFL1, and AHCTF1, are associated with overall survival in patients with TNBC.

In a separate analysis published in Genome Medicine, investigators generated a high-resolution single-cell atlas using 129,433 cells from 14 patient-derived xenograft models of TNBC with residual disease following neoadjuvant chemotherapy. Unsupervised clustering identified four transcriptionally distinct cancer cell states shared across the models, enriched in developmental, hypoxia, interferon signalling, chromosomal instability, and DNA damage-related pathways. Two of the identified cell states, linked to hypoxia and interferon signalling, shared transcriptional features associated with drug-tolerant persister cells. The hypoxia-related populations showed no association with mutation status, suggesting that resistance mechanisms may be driven through epigenetic rather than genetic pathways. Validation across multiple independent TNBC cohorts confirmed that the dysregulated pathways observed in residual disease were already present in chemotherapy-naïve tumors, and the cell states persisted in distant metastatic disease and were associated with prognosis and treatment response. Functional in vitro experiments showed that inhibition of the lysine demethylase KDM5B suppressed the emergence of drug-tolerant persister cells, indicating that epigenetic modulation could help prevent resistance development in TNBC.

Triple-negative breast cancer is a subtype of breast cancer constituting approximately 15–20% of all breast cancer cases, defined by the absence of estrogen receptor, progesterone receptor, and HER2 expression, and has the most aggressive behavior and the worst prognosis.