New ways of looking at tumor genetics and dynamics have been developed: the Liquid Biopsy (LB), which has been incorporated into clinical practice as a noninvasive analysis of circulating material derived from tumors, which represents an innovative tool in precision oncology and overcomes the current limitations associated with tissue biopsies. An LB is a new tool of great value, constituting a diagnostic, prognostic, and predictive marker. The elements that makeup LB are circulating tumor cells (CTCs) and circulating tumor nucleic acids (ctNA: DNA or RNA) in free cells or contained in exosomes, microvesicles, and platelets. The ctDNA and CTCs are the only one’s components with a clinical application approved by the US Food and Drug Administration (FDA).