IL4 and breast cancer: Indeed, the breast cancer TME is infiltrated by regulatory T cells [7, 8], myeloid-derived suppressor cells (MDSCs) [9, 10], and rich in inhibitory/Th2-polarized cytokines such as IL4 [11–13], that promote tumor survival [14–17], migration and invasion [18, 19], and directly inhibit Th1-polarized effector T cells [20, 21].