HER2/neu Immunostaining in Invasive Breast Cancer: Analysis of False Positive Factors

Area of Science:

• Oncology
• Pathology
• Molecular Diagnostics

Background:

• HER2/neu gene amplification and protein expression are crucial for breast cancer prognosis and Trastuzumab treatment.
• Immunohistochemistry (IHC) for HER2/neu protein can yield false positives, impacting treatment decisions.
• Fluorescent in situ hybridization (FISH) is more specific and sensitive for HER2/neu gene amplification than IHC.

Purpose of the Study:

• To investigate factors contributing to false positive HER2 IHC results.
• To identify reasons why HER2 IHC (3+) cases lack HER2/neu gene amplification by FISH.

Main Methods:

• Retrospective analysis of 18 invasive ductal carcinoma cases with HER2 IHC (3+) but no gene amplification by FISH.
• Histological review to evaluate technical errors (e.g., staining artifacts) and interpretation errors.

Main Results:

• Polysomy 17 was not detected in any of the studied cases via FISH.
• Five of 18 cases (27.8%) showed purely interpretation errors.
• The remaining cases had a combination of technical and interpretational errors leading to false positives.

Conclusions:

• Technical and interpretational errors in HER2 IHC testing can be minimized through enhanced education for technologists and pathologists.
• Accurate HER2 testing is vital to prevent incorrect therapeutic selections for breast cancer patients.
• High-quality immunostaining and accurate diagnostic interpretation are essential for effective breast cancer treatment.