Clinicopathological Study of Breast Carcinoma Patients with Equivocal HER2 Immunohistochemical Status: Five-Year Experience from a Tertiary Care Center.

Background and objectives: Assessment of HER2 gene status has central role in the management of breast cancer patients. For determining HER2 status, immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) are the most commonly used tests. Immunohistochemistry scores of 3+ and 1+ were considered as HER2 positive and negative, respectively. On the other hand, HER2 equivocal cases need further confirmation by FISH test assessment. This study aimed to identify the clinicopathological characteristics of patients with HER2 equivocal tumors served by Sultan Qaboos University Hospital (SQUH) in Muscat, Oman, with emphasis on treatment plans and disease outcome.

Methods

This was a retrospective cross-sectional study, which involved all breast cancer female patients who were referred to SQUH from 2016 to 2020. It included a total of 108 patients who were diagnosed with HER2 (2+) breast cancer. Patients' data were analyzed in relation to the subsequent FISH status.

Results

During the study period, data from 108 females with HER2 2+ were collected; among them, 22 (20%) were FISH positive, 64 (59%) FISH negative, 17 (16%) FISH borderline and five (5%) with no results. Regarding patients' characteristics, 91.2% of all subjects had invasive ductal carcinoma, 93.2% expressed estrogen receptors and 77.6% progesterone receptor. Age, postmenopausal histopathology, tumor grade, TNM staging, ER, PR, Ki67, LVSI, NLR, treatment and follow-up did not show significant association with different FISH results.

Conclusions

The majority of HER2 equivocal breast cancer cases were FISH negative. In trastuzumab chemotherapy, an association between different FISH results was expected.