STAT3 and breast cancer: The pro-tumor properties of Th17 cells in BC (Figure 2) are attributed to multiple mechanisms, including the regulation of angiogenesis, induction of pro-invasive factors (i.e., IL-17, IL-22, and IL-23), metalloproteinases (MMPs) that promote proliferation, survival, and the invasion of malignant cells, interfering with CD8+ T-cell migration through the activation of STAT3 signaling and subsequent reduction of CXCR3 expression [57,58,59,60].