HER2 positivity in patients with estrogen receptor (ER) positive breast cancer: Is it really prognostic?

Li et al. recently reported that HER2 positivity was associated with a better disease-free survival (DFS) (hazard ratio [HR], 0.38; 95% confidence interval [CI], 0.22–0.67; P = 0.001) and overall survival (OS) (HR, 0.40; 95% CI, 0.17–0.95; P = 0.037) [1]. While this was a large retrospective study (n = 1306), it is worth noting that patients with ER positive HER2 negative breast cancer treated without chemotherapy (n = 872) were excluded from the analysis.

This selection criteria led to subsequent inclusion of patients who were deemed high risk ER positive HER2 negative breast cancer to recommend adjuvant chemotherapy, and therefore, had a higher risk of relapse and death. Previous studies that examined the outcomes of all patients with ER positive breast cancer based on expression of HER2 reported a higher risk of relapse and worse survival outcomes in those with HER2 positivity [2,3]. Furthermore, HER2 expression has been associated with resistance to endocrine therapy in patients with ER and HER2 positive breast cancer, which further explains the worse outcomes in this population [4].

Therefore, authors may consider reporting DFS and OS of all patients with ER positive HER2 negative breast cancer additionally. This is likely to reflect the true impact of HER2 positivity on prognosis.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Declaration of competing interest

All the authors declare no competing conflict of interest relevant to this research article.