Diagnostic Accuracy of Immunohistochemistry for HER2-Positive Breast Cancer

Currently, human epidermal growth factor receptor 2 (HER2)-positive breast cancer cells are diagnosed under the American Society of Clinical Oncology (ASCO) and College of American Pathologists (CAP) 2018 guidelines. The guideline combined the results of in situ hybridization (DISH) and immunohistochemistry (IHC) techniques. The IHC technique is easy, cheap, and suitable for developing country. Therefore, in this study, we validated the use of IHC alone compared to the results of HER2 amplification under ASCO/CAP 2018 guidelines in diagnosed HER2 positive breast cancer cells.

A total of 510 breast cancer tissue samples from Rajavithi Hospital in Bangkok, Thailand, from January 1st, 2022, to May 31st, 2023, were analyzed by IHC, followed by dual ISH (DISH). We selected 58 samples of IHC equivocal (score 2+) and 98 samples of IHC positive (score 3+) to analyze the diagnostic values by comparing them to the results of HER2 amplification.

The HER2 IHC score was found to agree with HER2 amplification with a sensitivity of 87.96%, a specificity of 93.75%, a positive predictive value of 96.94%, a negative predictive value of 77.59%, a positive likelihood ratio of 14.07, a negative likelihood ratio of 0.13, and an accuracy of 89.74%.

The promising outcomes suggest that a positive IHC test result (score 3+) could potentially stand alone for patients with breast cancer undergoing anti-HER2 treatment, even without DISH confirmation.