AJSP2106 - CME/CMLE - Detailed Reanalysis of 500 Breast Cancers With Equivocal HER2 Immunohistochemistry and Borderline ERBB2 Fluorescence In Situ Hybridization Results-Detailed Reanalysis of 500 Breast Cancers With Equivocal HER2 Immunohistochemistry and Borderline ERBB2 Fluorescence In Situ Hybridization Results

Detailed Reanalysis of 500 Breast Cancers With Equivocal HER2 Immunohistochemistry and Borderline ERBB2 Fluorescence In Situ Hybridization Results

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The article discusses a study investigating the impact of reflex testing on breast cancer cases with equivocal HER2 status, following ASCO/CAP guideline recommendations. The study involved retesting 500 samples with borderline ERBB2 FISH results and equivocal HER2 IHC from external labs. Results showed changes in 37% of cases, mostly due to discordant IHC results. FISH rescoring changed ERBB2 status in 64 cases, with differences in FISH scores mainly small. Sequential testing with IHC and FISH rarely identified significant differences in ERBB2 status. Challenges in coordinating repeat testing were highlighted, but detailed reanalysis of challenging cases is considered clinically impactful. The study also highlighted the evolution of guidelines for interpreting borderline HER2 results in breast cancer, emphasizing the importance of precise methods in determining HER2 status for targeted therapy decisions. Overall, the study suggests that HER2 targeted therapies should be reserved for cases with positive IHC/FISH results, considering the high cost and potential cardiotoxicity of these treatments.

Keywords

reflex testing

breast cancer

equivocal HER2 status

ASCO/CAP guidelines

ERBB2 FISH

IHC results

repeat testing

targeted therapy decisions

HER2 targeted therapies

cardiotoxicity