The phenomenon of cell-free nucleic acids (cfNA) circulating in plasma has opened new areas of research for the study of the pathobiology of many diseases, particularly cancer. The detection, quantitation and qualitative analysis of such cfNA have had an increasing interest and utility for diagnosis and management of many kinds of cancer, at least as complementary tools. The origin of cfNA is not yet established, although it is probable that there are more than one. The study of microparticles and microvesicles containing cfNA surely will shed more light on this issue. In the present article, we reflect on some of these issues and review the evidence that supports the Theory of Genometastasis, which attributes a biologic role of cfNA in tumor progression by oncogenesis of host cells.