Abstract 1367: Comprehensive characterization of cell-free tumor DNA in plasma and urine of patients with renal tumors

Abstract

Abstract Renal cell carcinoma (RCC) represents a heterogenous disease in terms of histologic subtypes, prognosis and treatment response. Genetic heterogeneity offers a particular challenge to direct available targeted therapies that best match the patient. Profiling and monitoring of tumor-specific alterations from body fluids has been demonstrated as a valuable tool for many tumor types. Yet, the utility of circulating tumor DNA (ctDNA) in RCC has not been well established. To characterize the levels and composition of ctDNA in the plasma and urine we employed a broad range of targeted and untargeted methods to two independent cohorts of patients with renal tumors. We applied shallow Whole Genome Sequencing (sWGS) and modified Fast Aneuploidy Screen Test-Sequencing System (mFAST-SeqS) to 43 patients with metastatic RCCs. Using the mFAST-SeqS, ctDNA was detectable in only 2 out of 43 patients (4.7%). However, assessment of tumor fractions based on sWGS using the ichorCNA algorithm revealed 6 further patients with detectable amounts of ctDNA. In silico size selection of fragments < 150bp further improved the detection rate to 27% (12 out of 43 patients). This is consistent with previous reports that tumor-derived fragments are often smaller compared to cell-free DNA of normal cells and as such enrichment of smaller fragment increases the sensitivity. High-resolution mutation analysis of 10 recurrently mutated genes in RCC was performed using a QIASeq custom capture panel, enabling detection of tumor-specific mutations at baseline in 18% (8/43) of patients. Of these five had detectable tumor fractions as observed with ichorCNA. Furthermore, we had access to longitudinally obtained plasma samples for 37 of our 43 (86%) patients with a median follow-up period of 6 months (range, 0.4-19.2). The QIASeq panel was applied to follow-up patients of which mutations were identified at baseline. For most of these patients, ctDNA was elevated at treatment initiation but decreased with response. At the time of progression, or when a response could not be achieved, ctDNA increased or remained elevated. Plasma and urine samples were available for a second cohort (n=47) of patients with a wide range of renal tumors. Detection rates using both broad, untargeted sequencing methods and targeted, sensitive approaches were similarly low with 7/47 (14.9%) and 45.5% (10/22), respectively. Interrogation of those patients with detectable ctDNA revealed, for the first time, that urine ctDNA is capable of overcoming genetic heterogeneity and offers information that is complementary to that provided by plasma. Taken together, our data revealed that ctDNA levels are lower in RCC than other cancers of similar stage. Although, ctDNA can be detected in blood and urine of RCC patients and there is potential for clinical utility, improved isolation and detection methods are needed to achieve a broad patient coverage. Citation Format: Tina Moser, Christopher G. Smith, Maximilian Seles, Gabriel Wcislo, Matthew Eldridge, Samantha Perakis, Florent Mouliere, Isaac Lazzeri, Katrin Heider, Anne Warren, Nitzan Rosenfeld, Grant D. Stewart, Ellen Heitzer. Comprehensive characterization of cell-free tumor DNA in plasma and urine of patients with renal tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1367.