The Correlation between Immunohistochemistry and In Situ Hybridization for the Assessment of Human Epidermal Growth Factor Receptor 2 (HER-2) Status in Breast Cancer in Buddhasothorn Hospital

Objective: To investigate the correlation of immunohistochemistry (IHC) and in situ hybridization (ISH) for the assessment of human epidermal growth factor receptor 2 (HER-2) in breast cancer in Buddhasothorn Hospital. Materials and Methods: The present study design was a retrospective study. Breast cancer patients aged 18 years or older, diagnosed with stage I to IV according to the American Joint Committee on Cancer (AJCC) Eighth Edition between January 1, 2018 and September 30, 2023, in Buddhasothorn Hospital and had IHC and ISH for the assessment of HER-2 according to the American Society of Clinical Oncology and the College of American Pathologists (ASCO/CAP) 2018 were included. There were 131 breast cancer patients. Results: The present study included 131 breast cancer patients with average age of 54 years, tumor size greater than 20 mm but not exceeding 50 mm (T2) at 45.4% (59/131), and 1 to 3 lymph nodes involvement (N1) at 34.6% (45/131). Early breast cancer was presented in 83.2% (109/131) of the cases, with estrogen receptor positivity at 42% (55/131). HER-2 testing by IHC showed equivocal (2+) in 52% (68/131) and positive (3+) in 48% (63/131). The Ki-67 proliferation index was 34±21.6%. The result of HER-2 testing by IHC positive (3+) highly correlates with ISH at 96.83% (61/63), which was statistically significant (Spearman’s rho=0.54, p<0.001). The result of HER-2 testing by IHC positive (2+) correlated with ISH at 48.53% (33/68). These data demonstrated a correlation of HER-2 testing by IHC positive (3+) and ISH. Conclusion: The HER-2 test using the IHC method at Buddhasothorn Hospital in the IHC positive (3+) group had a statistically significantly high correlation with the ISH test. Therefore, there is no need for ISH testing. In the IHC equivocal (2+) group, the correlation with ISH results did not differ from other studies. This needs to be verified using ISH according to the standard.