Kopp et al. retrospectively studied 22 patients with BMM of breast cancer, 50% (11/22) were molecularly typed as hormone receptor (HR) positive and human epidermal growth factor receptor 2 (HER-2) negative (Kopp et al., 2011), Sakin et al. found similar results (21/30, 70%) (Sakin et al., 2020). The gene discussed is ERBB2; the disease is breast cancer.