STCube Reports Promising Phase 1b Results for BTN1A1-Targeted Therapy in Metastatic Colorectal Cancer
Key Insights
STCube (search)'s Nelmastobart, an anti-BTN1A1 (search) immune checkpoint inhibitor, demonstrated encouraging clinical activity with partial responses in 2 out of 5 patients with high BTN1A1 expression in metastatic colorectal cancer.
The Phase 1b study revealed that 83% of patients exhibited high BTN1A1 (search) expression (TPS≥50), supporting a biomarker-based patient selection strategy for the ongoing Phase 2 trial.
No toxicity related to Nelmastobart was observed, and all patients continued to benefit from treatment at the 4-month assessment with no cases of progressive disease reported.
STCube (search) has announced promising initial results from its Phase 1b clinical trial of Nelmastobart, an anti-BTN1A1 (search) immune checkpoint inhibitor, in patients with metastatic colorectal cancer. The biotech company will present these findings at the American Society of Clinical Oncology Gastrointestinal Cancers Symposium (ASCO GI) in San Francisco from January 8-10, 2026.
Clinical Efficacy and Safety Profile
The Phase 1b portion of the study enrolled all-comer patients without BTN1A1 (search) screening and demonstrated encouraging clinical activity. Partial response was observed in 2 out of 5 patients with BTN1A1 TPS≥50, while the remaining patients exhibited decreasing stable disease, indicating a trend toward tumor reduction. Notably, no toxicity related to Nelmastobart was observed throughout the study.
At the second tumor assessment conducted at the 4-month mark, all patients continued to benefit from the treatment, with no cases of progressive disease reported. This sustained clinical benefit supports the therapeutic potential of targeting BTN1A1 (search) in this patient population.
Biomarker-Driven Patient Selection Strategy
A key finding from the Phase 1b study was that 5 out of 6 patients (83%) exhibited high BTN1A1 (search) expression with a Tumor Proportion Score (TPS) ≥50. This high frequency of BTN1A1 expression in metastatic colorectal cancer patients has informed STCube (search)'s biomarker-based approach for the ongoing Phase 2 trial, which enrolls only patients with BTN1A1 TPS≥50.
The researchers evaluated BTN1A1 (search) expression alongside various tumor and immune-related biomarkers, including PD-L1 (search), CD8 (search), Ki-67, SLFN11, CK, and YAP1, strengthening the biological rationale for BTN1A1-based patient selection. According to STCube (search), BTN1A1 shows even higher expression levels in third-line patients who have failed previous chemotherapy.
Novel Immune Checkpoint Target
BTN1A1 (search) represents an immune checkpoint protein independently discovered by STCube (search) that suppresses CD8 (search) T cell activity within the tumor microenvironment. The company has confirmed across various tumor models that blocking BTN1A1 can enhance anti-cancer immune responses. BTN1A1 is being developed as a next-generation immune checkpoint target to overcome the limitations of PD-1/PD-L1 (search) therapies.
Combination Therapy Approach
STCube (search) is currently conducting a Phase 1b/2 clinical trial of Nelmastobart in combination with trifluridine-tipiracil (search) (TAS-102) and bevacizumab for metastatic colorectal cancer. The Phase 2 trial has shown rapid enrollment progress, with 18 out of the target 52 patients beginning treatment within just two months of initiation. The company aims to complete enrollment within this year.
Global Collaboration Strategy
An STCube (search) representative explained that the clinical data from both the current Phase 1b study and previous investigator-initiated trials consistently show clear treatment responses in patients with high BTN1A1 (search) expression. This evidence is being used for designing biomarker-based Phase 2 trials and for discussions on global collaboration.
The company plans to leverage the ASCO GI presentation to share its BTN1A1 (search)-targeted immuno-oncology platform and clinical strategy with global pharmaceutical companies and researchers. STCube (search) will also participate in the JP Morgan Healthcare Conference immediately following the symposium to discuss specific partnership options and development strategies.
The promising clinical results and biomarker validation data position Nelmastobart as a potential new treatment option for patients with metastatic colorectal cancer, particularly those who have exhausted standard therapeutic options.