OC_337_p
For each sampling time point, whole blood (9 mL) was collected in cfDNA collection tubes (Dxome, Seongnam, Republic of Korea). Cell-free DNA (cfDNA) was extracted from plasma samples (3â€“4 mL) using the Magnetic Serum/Plasma Circulating DNA Kit (Dxome, Seongnam, Republic of Korea). The size of the cfDNA was measured using TapeStation 4200 (Agilent Technologies, Santa Clara, CA, USA). cfDNA concentration was measured using a Qubit 3.0 Fluorometer (Thermo Fisher Scientific, Waltham, MA, USA). The resulting DNA was ligated using Illumina adapters and then indexed using unique dual indices for duplex sequencing (Illumina, San Diego, CA, USA). Sequencing libraries were hybridized with customized probes targeting nine ovarian cancer-related genes (TP53, BRCA1, BRCA2, ARID1A, CCNE1, KRAS, MYC, PIK3CA, and PTEN), which are frequently mutated in ovarian cancer.