HER2 Immunohistochemical Scores Provide Prognostic Information for Patients with HER2-type Invasive Breast Cancer

AimsInvasive breast cancer patients with human epidermal growth factor receptor 2 (HER2) immunohistochemical (IHC) scores of 3+ or 2+ with reflex in‐situ hybridisation (ISH) positivity are suitable for anti‐HER2 therapies. The aim of this study is to investigate whether the prognoses between IHC 3+ patients and IHC 2+/ISH+ patients are different.Methods and resultsWe analysed the clinicopathological information of 886 consecutive cases of HER2‐positive early breast cancer. The influences of the patients’ age, cancer stage, hormone receptor status and anti‐HER2 treatment were adjusted using a multivariate Cox regression model. Both HER2 copy numbers and HER2 ISH ratios of the IHC 3+ group were significantly higher than those of the IHC 2+/ISH+ group. The outcomes of IHC 3+ patients were significantly better than those of IHC 2+/ISH+ patients in the univariate and multivariate analyses. HER2 copy numbers of ≥8 represented the best prognostic value, and it was chosen to be the cut‐off value. The reflex ISH for IHC 2+ patients with high HER2 copy numbers (≥8) predicted a better overall survival than that for those with low HER2 copy numbers.ConclusionHER2 IHC scores and HER2 copy numbers can provide prognostic information for patients with HER2‐positive invasive breast cancer. Both IHC 3+ and IHC 2+ patients with high HER2 copy numbers had a better prognosis.