HER2 Testing in Breast Cancer: Correlation between Immunohistochemistry and FISH Using the Updated 2023 ASCO/CAP Guidelines
Keywords:
ASCO/CAP 2023, Breast cancer, Dual-probe ISH, FISH, HER2, IHCAbstract
Background Human epidermal growth factor receptor 2 (HER2) is an important prognostic and predictive marker in breast cancer patients. HER2 amplification status is a prognostic factor for the response to HER2-targeted therapy. HER2 status can be screened via immunohistochemistry (IHC). HER2 gene amplification can be detected by fluorescence in situ hybridization (FISH) according to ASCO/CAP 2018 guidelines. In 2023, the ASCO/CAP guidelines for HER2 testing by FISH were updated. We analyzed the correlation between HER2 IHC status and FISH-HER2 expression according to updated guidelines. Methods Female patients with histologically confirmed invasive breast cancer were enrolled at Chulabhorn Hospital. HER2-IHC staining was performed and interpreted according to the 2023 ASCO/CAP guidelines. Equivocal (2+) or positive (3+) IHC results were confirmed with FISH testing. Results A total of 263 patients was classified into 192 patients in the HER2-IHC 2+ group and 71 patients in the HER2-IHC 3+ group. Among patients in the HER2-IHC 2+ group, 138 had negative FISH results, and 54 had positive FISH. Results All 71 patients with IHC 3+ had positive HER2 FISH results. Our study revealed a statistically significant relationship between positive (3+) IHC and FISH for HER2, with a correlation rate of 100% in the IHC 3+ group (rs=0.639, p<0.001) and 28% in the equivocal (2+) IHC group. Conclusion In accordance with the 2023 ASCO/CAP recommendations, our findings support that FISH testing is not required for patients with HER2 IHC 3+ breast cancer, which may help expedite therapeutic decision-making and treatment initiation.
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