Ellen Heitzer is molecular geneticist, who is involved in both routine diagnostics of hereditary diseases and research. Her research focus on the analysis of circulating tumor DNA (ctDNA) and cells (CTC), often referred to as “liquid biopsy”. Applications of the liquid biopsy for clinical purposes are manifold as the concept of using blood represents a promising tool to track down tumor-specific changes during the entire course of the disease. A liquid biopsy can be used to identify surrogate indicators for disease recurrence as well as disease progression and can indicate if a specific treatment is applicable or will reduce the risk of recurrence or progression. In addition, the analysis of ctDNA and CTCs might provide important insights into tumor heterogeneity and progression. Currently Ellen Heitzer investigates the use of liquid biopsies in solid cancers as a tool for monitoring treatment response and the identification of resistance mechanisms.