STAT3 plays a crucial role in tumor development, thanks to its ability to regulate the transcription of the genes involved in the cell cycle (CCND1 (cyclin D), CCNE1 (cyclin E), and RAC1), cell survival (BCL2, BCLXL, HSP70 and FAS), metabolism (OCT1, HIF1A), chemoresistance (COX-2, MYC, OCTO-4, ABCC2, and ABCC6), immunosuppression (IL-10, IL-23, IL-6, and TGFB), angiogenesis (VEGFA and bFGF), migration and invasion (MMP1, 2, 3 and TWIST1), and stem cell phenotypes (MYC, SOX-2, and NANOG), among other mechanisms (Figure 3) [96,97]. The gene discussed is HIF1A; the disease is neoplasm.