PIK3CD and posterior cortical atrophy: To date, this is the first comprehensive study to validate the PIK3CD-S/PIK3CD-L profiles in a panel of PCa patients and cell lines, evaluate the functional impacts of PIK3CD-L and PIK3CD-S in PCa invasiveness/apoptosis, perform the molecular docking of drugs with PI3Kδ-L and PI3Kδ-S, validate the physical interaction of the ATP/drug with PI3Kδ-L and PI3Kδ-S, identify the SRSF2-mediated splicing mechanism for PIK3CD-S synthesis, and develop a novel synergistic drug therapy to overcome the Idelalisib resistance in AA PCa.