Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz

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Gewählte Publikation:

Moser, T.
Minimal-invasive therapy monitoring in plasma DNA of patients with metastasized renal cell carcinoma
PhD-Studium (Doctor of Philosophy); Humanmedizin; [ Dissertation ] Graz Medical University; 2021. pp. 110 [OPEN ACCESS]


Autor*innen der Med Uni Graz:
Balic Marija
Heitzer Ellen
Rinner Beate

Liquid biopsy, which refers to the minimally invasive analysis of circulating tumor markers from blood and other bodily fluids, represents an innovative tool for detecting and monitoring cancer-specific alterations. In particular, the analysis of circulating tumor DNA (ctDNA) has great clinical potential and has already been applied in many solid tumors to monitor treatment response and therapeutic effectiveness. However, the utility of ctDNA in renal cell carcinoma (RCC) is largely lagging behind. Extensive pathological and genetic heterogeneity is inherent to RCC, which confounds treatment decisions and is a significant hurdle in precision medicine. Here, we aimed to establish the potential utility of ctDNA in the clinical management of RCC by characterizing the levels and composition of ctDNA in patient body fluids. A major focus was on those patients who received targeted therapies to validate the ability of ctDNA to track the disease course longitudinally. Firstly, we focused on the optimization of ctDNA detection strategies. To this end, we aimed to enrich ctDNA fragments based on fragment length, which is reported to be shorter than cell-free DNA (cfDNA) from hematopoietic cells. In silico size selection improved ctDNA detection, with a more than two-fold median enrichment in particular cases. Secondly, we undertook a detailed analysis of baseline and longitudinal plasma and urine samples using a series of state-of-the-art approaches across two independent prospective clinical cohorts representing the full clinical spectrum of renal tumors. We initially applied a combination of untargeted methods and in silico size selection to plasma samples derived from metastatic RCC (mRCC) patients. We observed lower ctDNA levels in RCC relative to other solid cancers of similar size and stage, detecting plasma ctDNA in 32.6% of patients. The use of a high-resolution de novo mutation calling assay by targeting the ten commonly mutated genes in RCC did not improve detection beyond that obtained by untargeted methods (18.6%). Moreover, broad untargeted sequencing approaches applied to plasma and urine samples from the second cohort of patients indicated similarly low detection rates (39.6%). However, high-resolution personalized assays improved detection rates with incremental success (~50%). Overall, ctDNA detection in plasma was more likely amongst patients with larger tumors and in those with venous tumor thrombus. Despite the relatively low detection rates, our data revealed novel insights into the capabilities of ctDNA for minimally invasive assessment of RCC tumors. In particular, analysis of > 200 longitudinal plasma samples revealed that ctDNA dynamics widely fluctuated in accordance with disease course and thus may be used for therapy monitoring in RCC. Finally, further interrogation of those patients with detected ctDNA revealed that plasma and, for the first time, urine ctDNA may better represent genetic heterogeneity than a single tissue biopsy. In summary, our findings confirm RCC as a ctDNA-low malignancy. Nevertheless, these comprehensive results provide an important insight into the biology of renal cell carcinoma and contribute to the realization of precision cancer medicine, which is considered a promising tool in oncology.

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