FKBP4 is an immunophilin protein with peptidyl-prolyl isomerase and co-chaperone activities that functions as a critical regulator of multiple cellular pathways. Primary function involves interaction with heat shock protein 90 (HSP90) through tetratricopeptide repeat domains to regulate steroid receptor signaling 1. FKBP4 promotes glucocorticoid receptor (GR) activity in neurons by forming FKBP4-GR-HSP90 complexes and displacing FKBP5, with implications for hypothalamic-pituitary-adrenal axis function in stress-related psychiatric disorders including bipolar disorder 2. Mechanistically, FKBP4 orchestrates multiple signaling cascades: it potentiates IKK/NF-κB signaling through HSP90-mediated IKK complex assembly while facilitating Hsp70/RelA nuclear translocation 3, and suppresses p53 protein stability to promote hepatocellular carcinoma glycolysis via the p53/HK2 pathway 4. The FKBP4-HSP90 interaction shows strong molecular association in colorectal cancer 5. Clinical significance is substantial: elevated FKBP4 expression correlates with poor prognosis in hepatocellular carcinoma and lung adenocarcinoma patients 43. FKBP4 promotes cancer cell proliferation, migration, and invasion in multiple malignancies 36. FKBP4 gene polymorphisms associate with glucocorticoid efficacy and health-related quality of life in systemic lupus erythematosus patients 7. These findings identify FKBP4 as a prognostic biomarker and potential therapeutic target for cancer and stress-related disorders.