PIK3CA and central nervous system cancer: Pterostilbene + sertraline + gefitinib synergistically reduced glioblastoma cell viability, migration, and glioma sphere formationStrong synergy observed in EGFR‐amplified glioblastomas, particularly with PIK3CA/PTEN mutationsSertraline induced S‐phase accumulation but unexpectedly activated MAPK signaling (pMEK, pERK), suggesting compensatory feedbackRNF11 identified as a potential biomarker for sertraline sensitivity, linked to its ubiquitin‐editing function