RESUMO
Background@#Guidelines for testing human epidermal growth factor receptor 2 (HER2) in breast cancer using fluorescence in situ hybridization (FISH) were released in 2018. These guidelines were jointly developed by the American Society of Clinical Oncology (ASCO) and the College of American Pathologists (CAP) to achieve a clearer designation of breast cancer HER2 status. Clinical correlation with other factors was also considered appropriate, especially for those cases classified under ISH groups 2, 3, and 4.@*Objective@#In this study, we examined clinicopathologic features among Filipino breast cancer patients whose HER2 status was reclassified based on the 2018 ASCO/CAP guidelines.@*Methodology@#One hundred and thirty-two (132) breast cancer cases with immunohistochemistry (IHC) equivocal results in the Medical City were enrolled from January 2017 up to December 2020. HER2 FISH results classified under groups 2, 3, and 4 were then re-evaluated for HER2-IHC status in accordance with the 2018 ASCO/CAP guidelines. The relationship between clinicopathologic features and HER2 status was analyzed using the Fisher exact test.@*Results@#Significant differences were found in histologic type, nuclear pleomorphism, mitotic rate, progesterone receptor (PR) status, and regional lymph node involvement among the reclassified ISH groups. In the conv+ group, the tumor cells did not involve the regional lymph nodes as compared to group 5, where the tumor cells were involved. The conv- group had a higher grade for nuclear pleomorphism, mitotic count, and overall Nottingham Histologic Grade than group 5. There was a significant association between progesterone receptors among the conv- group and group 1.@*Conclusion@#Filipino breast cancer cases whose HER2 status was reclassified to negative following the 2018 ASCO/CAP guidelines had statistically different clinicopathologic features from those classified as group 5.