Prognostically, Kaplan-Meier analysis (Kaplan-Meier plotter, https://kmplot.com) of expression cohorts of breast tumor showed that high ERBB2 mRNA expression levels correlate with poor relapse-free survival in endocrine therapy-treated, ER+ ERBB2+, breast cancer patients (Fig. 4C). This evidence concerns the gene ESR1 and breast cancer.