Toward liquid biopsies in cancer treatment: application of circulating tumor DNA

Circulating tumor DNA (ctDNA) refers to the fraction of cell-free DNA in a patient's blood originating from tumor cells. Increased knowledge about tumor genomics, improvements in targeted therapies, and accompanying advances in DNA-sequencing technologies have increased the interest in using ctDNA as a minimally invasive tool in cancer diagnostics and treatment. Especially, early tumor detection including identification of minimal residual disease and stratification of adjuvant therapy are promising approaches. Also, ctDNA showed to be reliable in treatment monitoring and can be used to assess therapy resistance due to the broad variety of tumor subclones captured in ctDNA. Therefore, using ctDNA in the clinical setting has the potential to improve therapeutic outcomes. In the present review, we summarize the status of ctDNA in oncology with focus of being an alternative to tissue biopsies in early detection and treatment monitoring.