Reevaluating HER2-null breast cancer using an enhanced HER2 immunohistochemistry protocol

Area of Science:

• Oncology
• Pathology
• Biomarker Discovery

Background:

• Human epidermal growth factor receptor 2 (HER2) status is critical for breast cancer classification and treatment decisions.
• The classification of HER2 immunohistochemistry (IHC) 0 remains ambiguous, impacting therapeutic strategies for HER2-low breast cancer.
• Accurate HER2 assessment is essential for optimizing targeted therapy selection in breast cancer patients.

Purpose of the Study:

• To reassess HER2 expression in HER2-null breast cancer cases using an enhanced HER2 IHC protocol.
• To evaluate the sensitivity and heterogeneity of HER2 detection with improved IHC methods.
• To explore the potential of enhanced protocols for refining HER2 classification and patient selection for HER2-targeted therapies.

Main Methods:

• Reassessment of 58 HER2-null breast cancer cases using an enhanced HER2 IHC protocol and the VENTANA OptiView detection system.
• Evaluation of HER2 expression based on membrane positivity rate (%) and staining intensity.
• Microscopic assessment for HER2-positive tumor cell percentage and digital image analysis for staining intensity quantification.

Main Results:

• Detectable membrane HER2 positivity was observed in all tumors initially classified as HER2-null.
• HER2 positivity rates ranged from 0.33% to 90%, revealing significant inter- and intratumoral heterogeneity.
• The enhanced HER2 IHC protocol demonstrated improved detection sensitivity compared to standard methods.

Conclusions:

• Enhanced HER2 IHC protocols can detect HER2 expression in cases previously considered HER2-null.
• These advanced methods may improve the accuracy of HER2 classification and identify patients eligible for HER2-targeted treatments.
• Further research is warranted to establish the clinical significance of HER2 expression detected by enhanced protocols.