If we consider the homogeneity of ERG rearrangement in circulating tumor cells (CTCs) [37] and that the ETS gene rearrangements occur early in the development of prostate cancer, as they are often seen in high-grade PIN [38], and, when observed, are present in all tumor cell within a nodule; then, we can consider this a possible marker of tumor clonality. The gene discussed is ERG; the disease is prostate carcinoma.