Single HER2-positive tumor cells are detected in initially HER2-negative breast carcinomas using the...

Area of Science:

• Oncology
• Genetics
• Molecular Biology

Background:

• HER2 overexpression in breast cancer (BC) is critical for anti-HER2 therapy selection.
• Current HER2 testing (IHC/FISH) faces challenges due to tumor heterogeneity and differences between primary tumors (PT) and circulating tumor cells (CTCs).
• A novel DEPArray™-PT-HER2-FISH workflow was developed to address these limitations.

Purpose of the Study:

• To establish and validate a DEPArray™-based workflow for precise HER2 gene amplification analysis in single breast cancer cells.
• To identify HER2-positive cells in patients with HER2-negative primary tumors but HER2-positive CTCs.
• To compare the diagnostic accuracy of the new workflow with conventional pathology methods.

Main Methods:

• Single-cell suspensions were prepared from FFPE tumor samples of validation and development cohorts.
• DEPArray™ technology was used for pure tumor cell isolation.
• HER2 gene amplification was assessed using fluorescence in situ hybridization (FISH) on isolated single cells.

Main Results:

• The DEPArray™-HER2-FISH workflow showed high concordance (81.6%–84%) with routine pathology.
• In the development cohort, 4 out of 25 patients with HER2-negative primary tumors were found to have HER2-positive cells via DEPArray™-HER2-FISH.
• Patients with discordant HER2 results (detected by DEPArray™-HER2-FISH but not routine pathology) had poorer survival outcomes.

Conclusions:

• The DEPArray™ system enables accurate HER2/neu FISH analysis of pure tumor cells, demonstrating high concordance with conventional methods.
• This workflow can identify HER2-positive cells missed by routine pathology in HER2-negative primary tumors.
• For HER2-negative patients with HER2-positive CTCs, this approach may facilitate access to anti-HER2 treatments, potentially improving patient outcomes.