What is the added value of digital image analysis of HER2 immunohistochemistry in breast cancer in clinical practice? A study with multiple platforms

Abstract

Aims

We aimed to compare digital image analysis (DIA) of HER2 immunohistochemistry (IHC) in breast cancer by two platforms; to validate DIA against standard diagnostics; and to evaluate the added value of DIA in clinical practice.

Methods and results

HER2 IHC and in‐situ hybridisation (ISH) were performed on 152 consecutive invasive breast carcinomas. IHC scores were determined with DIA using two independent platforms. Manual scoring was performed by two independent observers. HER2 status was considered positive in 3+ and ISH‐positive 2+ cases. HER2 status using DIA was compared to HER2 status with standard diagnostics (manual scoring with ISH in 2+ cases). Inter‐platform agreement of IHC scores was 'moderate' (linear weighted κ=0.58), agreement between manual scoring and platform A was 'moderate' (κ=0.60) and between manual scoring and platform B 'almost perfect' (κ=0.85). Compared to manual scoring, DIA resulted in a reduction of 2+ cases from 17.1% to 1.3% with platform A and from 17.1% to 15.8% with platform B. However, compared to standard diagnostics, there were three false‐negative cases with DIA using platform A (81.3% sensitivity, 100% specificity, 100% positive predictive value [PPV], 97.8% negative predictive value [NPV]). Sensitivity, specificity, PPV and NPV were 100% with DIA using platform B.

Conclusions

DIA of HER2 IHC is a valid tool in determining HER2 status in breast carcinoma. Algorithms in different platforms can behave differently and optimal calibration is essential. In clinical practice, DIA offers an objective alternative to manual scoring, but a reduction in 2+ cases could result in loss of sensitivity.

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