PIK3CA and neoplasm: Through redox-sensitive regulation of MAPK/ERK, PI3K/Akt/mTOR, JAK/STAT, HIF-1α, NF-κB, and Nrf2/Keap1 pathways, ROS orchestrate tumor cell proliferation, survival, metabolic reprogramming, immune evasion, and therapy resistance—highlighting oxidative signaling as a dynamic driver and therapeutic target in malignancy.