ABS-011 HER2 PET Tracer: Validated Heterogeneity Problem, Unproven Clinical Utility Bridge

Curium Acquires Abscint SA, Expands Oncology Radiodiagnostic Pipeline

Curium has completed the acquisition of Abscint SA, a Belgian clinical-stage radiopharmaceutical company. This transaction grants Curium global rights to ABS-011, an investigational gallium-68-labeled PET radiodiagnostic tracer targeting HER2. ABS-011 is designed to provide whole-body, quantitative imaging of HER2 expression, which is crucial in cancers like breast and gastric cancers. The tracer is currently being evaluated in the multicentered Phase 2b HERMIA trial (NCT 06369831) in Belgium, aiming to enhance patient characterization and guide optimal care.

• Curium's acquisition of Abscint SA significantly expands its radiodiagnostic capabilities and oncology footprint, securing global rights to ABS-011. This move reinforces Curium's commitment to advancing innovative radiopharmaceuticals for cancer patients, particularly in HER2-positive breast and gastric cancers, by integrating a promising diagnostic asset into its pipeline.
• ABS-011 is a gallium-68-labeled PET radiodiagnostic tracer utilizing a radiolabeled single-domain antibody to target HER2. Its design allows for rapid binding and quick clearance, enabling same-day, whole-body PET imaging. This provides a comprehensive view of HER2 expression across multiple lesions, potentially revealing spatial heterogeneity missed by single-lesion biopsies and guiding clinicians in selecting optimal biopsy sites and treatment strategies.
• ABS-011 is currently being evaluated in the multicentered Phase 2b HERMIA clinical trial in Belgium (NCT 06369831). Curium plans to leverage its extensive expertise in radiopharmaceutical development, manufacturing, and commercialization to support the continued advancement of ABS-011 towards regulatory approval and eventual patient access, building on Abscint's foundational work in differentiated HER2 imaging.

The Evolving Landscape of HER2 Biomarkers and Diagnostics

Accurate HER2 identification relies on a multimodal diagnostic framework combining protein expression and gene amplification assays, with criteria that have been iteratively refined across successive guideline updates. Testing algorithms differ meaningfully by tumor type, and evolving classification systems have had measurable impacts on positivity rates in real-world practice.

• IHC scoring as the primary screen: Immunohistochemistry assesses HER2 protein expression at the tumor cell membrane. In breast cancer, ASCO/CAP guidelines define HER2 positivity as IHC 3+ (strong, complete membrane staining in >10% of tumor cells per 2013 criteria, reduced from 30% under 2008 criteria) or IHC 2+ with ISH-confirmed amplification. Gastric and gastroesophageal cancers use a modified scoring system, where IHC 3+ or IHC 2+/ISH-positive tumors are considered HER2 positive; interobserver agreement for this modified system is high (κ = 0.78).

• ISH-based amplification testing and guideline evolution: FISH and CISH quantify HER2 gene copy number. The 2013 ASCO/CAP guidelines set thresholds of HER2/CEP17 ratio ≥2.0 and average HER2 signals ≥6.0 per cell. The 2018 guidelines further stratified ISH interpretation into five groups (groups 1 and 3 classified as HER2 positive), resulting in a significant increase in ISH-negative calls by reclassifying previously equivocal cases. Relative to 2008 criteria, the 2013 update drove a 2% overall increase in HER2-positivity rate, largely attributable to a 3.5% increase in FISH-positive cases.

• Concordance between modalities: ASCO/CAP criteria yield superior IHC-to-FISH concordance compared to FDA criteria — 81% versus 75% in breast cancer using 2013 guidelines — underscoring the clinical significance of which scoring standard is applied.

• Tumor heterogeneity and staining pattern considerations: Over half (53%) of HER2-positive endometrial serous carcinomas exhibit significant heterogeneity of protein expression, necessitating evaluation across multiple tumor sections or large tumor areas. Additionally, the majority of HER2-positive endometrial tumors display a lateral/basolateral rather than apical membrane staining pattern, a morphological nuance with interpretive implications.

• Emerging genomic biomarkers — mutations and fusions: Beyond amplification, ERBB2 tyrosine kinase domain mutations have emerged as independently actionable targets across multiple solid tumor types. ERBB2 fusions, while less prevalent (0.28% of solid tumors overall), occur at higher rates in gastroesophageal junction cancer (3.12%), breast cancer (1.89%), urothelial carcinoma (1.72%), and gastric cancer (1.60%); notably, 75.28% of patients harboring an ERBB2 fusion also have concurrent ERBB2 amplification.

Curium's Strategic Bet on Precision HER2 Diagnostics

Curium's strategic acquisition of Abscint SA, bringing the gallium-68-labeled PET radiodiagnostic tracer ABS-011 into its pipeline, represents a forward-looking move in the evolving landscape of precision oncology. This investigational agent, currently in Phase 2b clinical trials, aims to provide whole-body, quantitative imaging of HER2 expression, a critical biomarker in several aggressive cancers, including breast and gastric malignancies.

The ability to accurately and non-invasively characterize HER2 status across all tumor sites is paramount for guiding treatment decisions and optimizing patient care. Traditional methods can be limited by tumor heterogeneity or accessibility, and the dynamic nature of HER2 expression, which can change over time or with treatment, underscores the need for advanced imaging solutions. PET imaging, known for its superior sensitivity and resolution, offers a promising avenue to address these challenges, potentially providing a more comprehensive picture of a patient's disease.

However, this strategic expansion is not without its considerations. As with any clinical-stage asset, ABS-011 faces the inherent risks of late-stage clinical development. The Phase 2b HERMIA trial will be crucial in demonstrating robust diagnostic accuracy and a favorable safety profile in a larger patient cohort. Radiopharmaceuticals require meticulous evaluation of radiation dosimetry to ensure patient safety, with studies on similar agents highlighting the importance of monitoring absorbed doses in organs such as the liver, kidneys, and spleen. Furthermore, ABS-011 will need to differentiate itself within a competitive diagnostic landscape, proving its clinical utility and superiority over existing or emerging HER2 assessment tools. Success in these areas could solidify Curium's position as a leader in advanced diagnostic imaging, paving the way for more personalized and effective cancer treatments.