STCube Initiates Phase 2 Colorectal Cancer Trial After Completing Phase 1b Without DLT

STCube announced on August 12 that it has initiated Phase 2 clinical dosing after successfully passing all safety assessments without any dose-limiting toxicity (DLT) in the Phase 1b trial of the combination therapy of Nelmastobart, trifluridine-tipiracil (TAS-102), and bevacizumab in patients with treatment-refractory colorectal cancer.

The Phase 2 trial is a biomarker-driven study targeting patients who are BTN1A1 expression positive.

In the Phase 1b trial, a total of six patients were enrolled in the starting dose cohort to assess drug toxicity of the combination therapy and to determine the recommended Phase 2 dose (RP2D).

According to the evaluation by the Safety Review Committee (SRC), the Nelmastobart combination therapy demonstrated a stable tolerability profile, with no unexpected adverse events or serious adverse events observed. Most treatment-related adverse events (TRAEs) were mild, at Grade 1 or 2, such as nausea and anemia. One out of the six patients experienced Grade 4 or higher neutropenia. However, this was attributed to trifluridine-tipiracil, and there were no accompanying adverse cases such as fever or infection.

Accordingly, in Phase 2, the standard doses of trifluridine-tipiracil at 35mg/m² and bevacizumab at 5mg/kg will be maintained, with Nelmastobart administered at 800mg in combination. Patient dosing for Phase 2 has already begun at Korea University Anam Hospital, and patient enrollment is expected to expand to multiple institutions, including Asan Medical Center, Seoul National University Bundang Hospital, Seoul National University Hospital, and Severance Hospital in Sinchon, during the third quarter of this year.

A representative from STCube stated, "Among the patients enrolled in Phase 1b, five were confirmed to have a BTN1A1 tumor proportion score (TPS) of 50 or higher, so they were included in the Phase 2 patient group (a total of 52 patients) without separate re-enrollment," adding, "By pre-screening for BTN1A1 expression in patients, efficient patient selection and enrollment have been achieved from the outset."

Unlike PD-L1, which is rarely expressed in colorectal cancer, the proportion of patients expressing BTN1A1 averages over 40%, indicating high target suitability. The BTN1A1-based precision clinical strategy is said to offer competitiveness in terms of both the clarity of the target patient group and market potential. In particular, adding an immuno-oncology agent to the standard third-line therapy of trifluridine-tipiracil and bevacizumab is expected to provide multiple therapeutic benefits for BTN1A1-positive patients, including improved tolerability, response rate, and survival.

A company representative commented, "Nelmastobart is the world's only immuno-oncology agent targeting BTN1A1 and has the potential to offer a new treatment option across a range of solid tumors," adding, "This Phase 2 trial in BTN1A1-positive patients will serve as key evidence to validate the biomarker's relevance and the efficacy of the targeted therapeutic strategy."

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