FKBP4 and lung cancer: As one of the most extensively studied proteins among the 18 identified human FK506-binding proteins (FKBPs), FK506-binding protein 4 (FKBP4), also known as FKBP52, has been reported to exhibit multiple functions which involve binding to different cellular receptors or targets in various kinds of cancers, such as lung cancer (15), prostate cancer (16), and glioblastoma (17).