Objectives. To determine by means of a systematic review, the effect of the liquid biopsy in the prevention, diagnosis and treatment of cancer, through the ctDNA marker. Methods. The most relevant studies published originally in the English language and Portuguese language between 2008 and 2018 were analyzed, with reference to the Scientific Electronic Library Online - SciELO and MEDLINE (National Library of Medicine) databases. Aiming to select the studies with the highest scientific evidence, we contemplated only controlled clinical research and randomized (ECCR) marker ctDNA. The search strategy used the following keyword combinations: liquid Biopsy, ctDNA Cancer. To identify the study designs, the following terms were used: clinical trials. Results. There were 1,394 studies involving liquid biopsy. However, only 25 were part of the ctDNA marker for evaluation in the present study. The studies were judged by the reviewers and after applying the criteria, only 18 were part of the scope of this review. Conclusion. This demonstrates confirms the efficacy of ctDNA marker analysis and the benefits of net biopsy in the therapeutic approach to cancer, improving patients' quality of life, as well as contributing to prevention and monitoring.