Androgen receptor (AR) is a member of the steroid receptor transcription factor family. In prostate cancer, increased levels of androgens in the tumor cells promote (1) AR signaling associated with cell-cycle regulation, growth, and survival, and (2) the expression of oncogenic fusion genes (including PSA, TMPRSS2, and hK2). Alterations in AR transcripts disrupt the open reading frame leading to the expression of truncated proteins that are not androgen dependent. AR-V7 is one of the splice variants of AR lacking the C-terminal LBD, but being constitutively active as a transcription factor and capable of promoting activation of target genes.