Background: ARA70 (androgen receptor-associated 70) was originally identified as part of chromosomal rearrangement involving the RET proto-oncogene. It was subsequently isolated in a two-hybrid screen as a ligand-dependent associated factor of the androgen receptor (AR). In addition to functioning as a co-activator of the AR, ARA70 has been found to function as a co-activator of the vitamin D receptor, estrogen receptor, PPARalpha, and PPARgamma.