Clinicopathological Characteristics of Breast Cancer Patients with Equivocal Immunohistochemistry: A Prevalence-Based Statistical Analysis.

Abstract

Background & objective: Although the concordance between immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) is generally high for HER2 scores of 3+ and 1+, discrepancies remain in cases scored as IHC 2+. This study aimed to evaluate HER2/neu gene amplification using FISH in breast cancer patients with IHC 2+ and to examine associated clinicopathological characteristics.

Methods: This retrospective study included tissue samples from 369 women diagnosed with invasive ductal carcinoma of the breast and an equivocal HER2 IHC score (2+). These samples were further assessed for HER2 gene amplification using FISH. Demographic and clinicopathological data were collected and analyzed.

Results: The mean age of patients was 51.6 ± 2.6 years. FISH analysis revealed no HER2 amplification in 72.6% of IHC 2+ cases, while 27.4% demonstrated amplification. HER2 amplification was significantly associated with younger age, higher histological grade, lymph node involvement, larger tumor size, and reduced survival rate. No significant association was observed between HER2 amplification and margin involvement.

Conclusion: HER2 amplification is a significant predictor of aggressive tumor behavior and may necessitate targeted therapy. In cases with IHC 2+, both FISH results and relevant clinicopathological features should be considered prior to initiating trastuzumab treatment.