Investigation of Equivocal Expression of HER2 Gene by Immunohistochemistry in Patients with Invasive Breast Ductal Cancer Confirmed by CISH or FISH and Its Relationship with Clinicopathologic Variables

Abstract

Objectives: The aim of this study was to determine the equivocal HER2 gene expression in patients with invasive ductal carcinoma of the breast approved by the chromogenic in situ hybridization (CISH) or fluorescence in situ hybridization (FISH) method and its association with clinicopathologic variables. Methods: This cross-sectional census-based study was conducted with information obtained by filling out questionnaires based on patient records or telephone contacts. Referring to the pathology lab archive, we extracted all immunohistochemistry (IHC) results related to the patients of breast cancer with HER2 2+ between 2011 and 2016. The patients’ information and the results of the CISH or FISH method were obtained, as well. Results: The mean age of 247 patients was 48.21 ± 11.33 years. The result of the complementary CISH or FISH test was negative in 124 (50.2%) patients and positive in 123 (49.8%) patients. There was a significant relationship between the age groups and CISH (P value < 0.05). In the age group of fewer than 29 years, there was the most likelihood of CISH positivity and in the age group of 60, there was the most likelihood of CISH negativity. There was a significant relationship between KI-67 status and CISH result. Our results revealed that false negative HER2 test was high. Conclusions: this result may be due to the type of the kit or antibody used or different guidelines used for the interpretation of the test. It is proposed to perform more precise complementary tests to determine the status of this gene. Moreover, laboratories should follow the ASCO/CAP guideline for HER2 evaluation in breast carcinoma.