When comparisons were available using FISH for all the tissues examined, CTCs, metastases and therapy-naïve primary prostate tumor tissues (cores obtained several years before, prior to any treatment) invariably had the same ERG gene status suggesting that (1) prostate biopsies are able to detect the tumor foci that result in blood-borne metastases, and (2) rearrangement of ERG gene may be an early event in prostate carcinogenesis [62]. The gene discussed is ERG; the disease is prostate neoplasm.