ERG and prostate cancer: In terms of gene expression responses and co-regulation, the TMPRSS2 gene (frequently regarded an androgen “specific” gene, found in an active fusion with the ERG oncogene in about 50% of prostate cancers) [53] was clearly upregulated by androgens (12 fold), as expected, in the luminal compartment, but showed an even higher upregulation (40 fold) within the basal compartment from a base state under the influence of retinoic acid [26,54].