There are three general categories of breast cancer: hormone receptor-positive (HR+), human epidermal growth factor receptor-positive (HER2+), and triple-negative (TN).313–315 Distant metastasis and therapy resistance are the root cause of the poor prognosis of the majority of patients with breast cancer.316,317 Accumulating evidence suggests that all the STAT family members are closely associated with breast cancer, having either pro-tumorigenic or antitumorigenic characteristics.318 Therefore, breast cancer provides an example of the double-edged sword role of JAK-STAT in carcinogenesis. The gene discussed is ERBB2; the disease is breast cancer.