Evaluation of HER2 Positivity Based on Clinicopathological Findings in HER2 Borderline Tumors in Iranian Patients with Breast Cancer

Background & Objective: Human epidermal growth receptor-2 (HER2) gene amplification is an important predictive and prognostic factor in breast cancer treatment. However, the expression of HER2 determined by immunohistochemistry (IHC) is considered as borderline in some cases, and confirmation of the HER2 status by either fluorescent in situ hybridization (FISH) or chromogenic in situ hybridization (CISH) is necessary for correct treatment decision-making. Considering the high cost of FISH and CISH, we aimed to investigate whether clinicopathological findings of the tumor could predict the HER2 status. Methods: A retrospective study was performed using the data from 584 patients with breast cancer with HER2-borderline disease, confirmed by IHC. Final HER2 status, pathologic tumor size and type, nodal involvement, Ki67 index, presence of estrogen and progesterone receptors (ER, PR), lymphovascular invasion (LVI), and stage were retrieved from the clinical records. Results: One hundred twenty-one (20.7%) patients were HER2-positive according to the FISH or CISH results. Logistic regression analysis showed that the pathologic size was positively associated with HER2 positivity with an odds ratio (OR) of 1.02 (95% CI: 1.01-1.04). In addition, the adjusted OR illustrated a statistically significant association between HER2 positivity and PR negativity (OR= 2.22, 95% CI: 1.29-3.83). Conclusion: In HER2 borderline breast cancer, HER2 positivity significantly increases with tumor size and PR negativity. Further studies are recommended that may find an applicable model to predict the actual status of HER2 in borderline cases.