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Analyses of genomic alterations in cell-free DNA (cfDNA) shed from tumors into the blood stream is rapidly advancing as a method to detect and genotype cancer. Liquid biopsy analyses are a favorable alternative to invasive tissue approaches, particularly for cancers in organs where tissue is difficult to obtain. As these methods become a clinical standard, the method for blood collection and plasma isolation will be an important consideration to ensure optimal assay performance with limited degradation of circulating tumor DNA (ctDNA). We compared blood collection and plasma isolation using both K2EDTA and cell-free DNA Streck™ BCT tubes to determine the stability of cfDNA and ctDNA in blood at room temperature or at 4°C. Blood was collected from nine cancer patients with KRAS mutations using K2EDTA and Streck™ BCT tubes. Over the course of seven days, cell lysis occurred in K2EDTA tubes at room temperature, releasing germline DNA into the blood (1300% increase over seven days), which significantly increased the number of total genomic equivalents. Additionally, we found that the volume of plasma collected from both tube types during blood fractionation decreased over time when tubes were at room temperature (an average of 3.5 mL vs. 1.0 mL, respectively). To evaluate the effect of storage conditions on performance of each tube type, blood was also collected from six cancer patients with KRAS or EGFR mutations and either maintained at room temperature or stored at 4°C for up to three days. Taken together, K2EDTA tubes stored at 4°C prevented cell lysis and preserved the ctDNA in a manner equivalent to Streck™ BCT tubes. These data demonstrate that liquid biopsies can be collected using either tube type with similar performance and appropriate consideration of storage conditions. Citation Format: Sonya T. Parpart-Li, Bjarne Bartlett, Maria Popoli, Vilmos Adleff, Julie Brahmer, Nilo Azad, Sarah Bonerigo, Ilene Browner, Amy Ryan, Victor Velculescu, Mark Sausen, Luis A. Diaz. Optimized plasma collection procedures for liquid biopsy analyses in cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3957.