JAK2 and breast cancer: Overexpression and constitutive activation/autophosphorylation of HER2 is associated with more aggressive disease and poor prognosis in patients with HER2pos BC.1 The activated HER2 protein recruits and regulates various intracellular signaling proteins PI3K/Akt, JAK2, STAT3 and STAT5 to induce cancer cell proliferation, differentiation, and survival in HER2pos BC.54–56 Trastuzumab treatment has been shown to block HER2-mediated PI3K/Akt signaling activation in HER2pos BC cells.