This review highlights the central importance of ROS-regulated signaling pathways—including MAPK/ERK, PI3K/Akt/mTOR, JAK/STAT, NF-κB, HIF-1α, and NRF2—in driving proliferation, survival, metabolic adaptation, immune evasion, and therapy resistance in tumor cells. The gene discussed is HIF1A; the disease is neoplasm.