Discordance between Equivocal HER2 Immunohistochemistry and Fluorescence in Situ Hybridization Analysis among the Breast Carcinoma Patients in Bangladesh: A Series of 75 Cases

Background: Accurate determination of HER2 status in breast carcinoma is essential for guiding targeted therapy and improving patient outcomes. While immunohistochemistry (IHC) is commonly used as an initial screening method, equivocal (2+) IHC results often require confirmation through fluorescence in situ hybridization (FISH). However, data on the concordance between IHC and FISH in Bangladesh remain limited, despite its significance in ensuring appropriate treatment planning. Materials and Methods : This retrospective observational cross-sectional study was conducted in the Department of Pathology in Ahsania Mission Cancer and General Hospital (AMCGH), Uttara, Dhaka, Bangladesh, from January 2024 to June 2025. The consecutive sampling technique was used and a total of 75 IHC-tested equivocal or borderline (2+) cases were retrospectively employed in this study. Breast tissue specimens were obtained via mastectomy (n = 10), and core needle biopsy (n = 65), processed into formalin-fixed paraffin-embedded (FFPE) blocks, and analyzed following ASCO/CAP guidelines. FISH analysis was performed on all cases (N = 75) to assess HER2 gene amplification. Then the data were extracted and analyzed using Statistical Package for Social Sciences (SPSS), version 23.0. Results : The average age of the patients was 48.3 ± 11.1 years, with a range of 28 to 88 years. Most patients were aged 38 to 47 years (36.0%), and specimens were predominantly acquired by core needle biopsy (86.6%). In tumor grading, cases (core needle biopsy, n = 65), 75.3% were classified as Grade II tumors. FISH analysis revealed HER2 amplification in only 4 cases (5.3%), while the majority (94.6%) were non-amplified despite initial IHC 2 + scoring. The difference between the IHC and FISH findings was statistically significant (p < 0.001), highlighting the risk of misclassification when relying solely on IHC. Conclusion : This study demonstrates substantial discordance between equivocal IHC and FISH findings in determining HER2 status among breast carcinoma patients in Bangladesh. These results reinforce the critical need for routine molecular confirmation using FISH in IHC 2 + cases to ensure accurate diagnosis and guide effective HER2-targeted therapy, ultimately improving clinical decision-making and patient care.