cancers Review Circulating Cell-Free DNA in Breast Cancer: Searching for Hidden Information towards Precision Medicine Maria Panagopoulou 1,*, Manel Esteller 2,3,4,5 and Ekaterini Chatzaki 1,6 1 Laboratory of Pharmacology, Department of Medicine, Democritus University of Thrace (DUTH), 68100 Alexandroupolis, Greece;
[email protected] 2 Josep Carreras Leukemia Research Institute (IJC), Badalona, 08016 Barcelona, Spain;
[email protected] 3 Centro de Investigacion Biomedica en Red Cancer (CIBERONC), 28029 Madrid, Spain 4 Institucio Catalana de Recerca I Estudis Avancats (ICREA), 08016 Barcelona, Spain 5 Physiological Sciences Department, School of Medicine and Health Sciences, University of Barcelona (UB), 08016 Barcelona, Spain 6 Institute of Agri-Food and Life Sciences Agro-Health, Hellenic Mediterranean University, 71003 Crete, Greece * Correspondence:
[email protected]; Tel.: +30-694-248-5045 Simple Summary: Our research focuses in the elucidation of the nature of circulating cell-free DNA (ccfDNA) as a biological entity and its exploitation as a liquid biopsy biomaterial. Working on breast cancer, it became clear that although a promising biosource, its clinical exploitation is burdened mainly by gaps in knowledge about its biology and specific characteristics. The current review covers multiple aspects of ccfDNA in breast cancer. We cover key issues such as quantity, integrity, releasing structures, methylation specific changes, release mechanisms, biological role. Machine learning approaches for analyzing ccfDNA-generated data to produce classifiers for clinical use are also discussed. Citation: Panagopoulou, M.; Esteller, M.; Chatzaki, E. Circulating Cell-Free Abstract: Breast cancer (BC) is a leading cause of death between women. Mortality is significantly DNA in Breast Cancer: Searching for raised due to drug resistance and metastasis, while personalized treatment options are obstructed Hidden Information towards by the limitations of conventional biopsy follow-up.