RESUMO
Cancer is a complex, heterogeneic, and dynamic disease involving multiple gene-environment interactions, and affecting numerous biological pathways. As such, the development of reliable and robust non-invasive platforms constitutes a vital step toward realizing the potential of precision medicine. Distant metastases harbor unique genomic characteristics that are not detectable in the corresponding primary tumor of the same patient, and metastases located at different sites show considerable intra-patient heterogeneity. Thus, the analysis of the resected primary tumor alone or, if possible, re-evaluation of tumor characteristics based on the biopsy of the most accessible metastasis, may not reveal sufficient information for treatment decisions. Here, we propose that this dilemma can be solved by a new diagnostic concept: liquid biopsy, that is, the analysis of therapeutic targets and drug resistance-conferring gene mutations in or on circulating tumor cells (CTCs). Finally, the analysis of the resected primary tumor alone may provide misleading information with regard to the characteristics of metastases, the key target for systemic anticancer therapy. Liquid biopsies are noninvasive tests using blood or fluids that detect CTCs or the products of tumors, such as fragments of nucleotides or proteins that are shed into biological fluids from the primary or metastatic tumors. Such biopsies are expected to be informative or easily accessible tools to provide comprehensive information regarding cancers beyond conventional biopsies. Thus, this review addresses the use of CTCs in cancer detection, diagnosis and monitoring and discusses the direction of its clinical application in cancer patient care.