Sequencing library construction and target enrichment
Before library construction, 1 μg each of genomic DNA extracted from PBL and tumor specimen was sheared to 300-bp fragments with a Covaris S2 ultrasonicator (Covaris, Woburn, MA, USA). A volume of 20–80 ng DNA from plasma were used for library construction. Indexed Illumina next-generation sequencing (NGS) libraries were prepared from PBL DNA and tumor DNA using the KAPA Library Preparation Kit (Kapa Biosystems, Wilmington, MA, USA).
Target enrichment was performed with a custom SeqCap EZ Library (Roche NimbleGen, Madison, WI, USA). To explore the comprehensive genetic properties of Chinese pan-cancer patients, the capture probe was designed based on ~1.04 Mb genomic regions of 1021 genes frequently mutated in common solid tumors. Capture hybridization was carried out according to the manufacturer’s protocol. Following hybrid selection, the captured DNA fragments were amplified and then pooled to generate several multiplex libraries.