Sample processing and DNA extraction
All fresh samples were stored in -80℃ refrigerators immediately till all sample collection was finished. Peripheral blood was collected in EDTA Vacutainer tubes (BD Diagnostics, Franklin Lakes, NJ, USA) and processed within 4 h. Peripheral blood lymphocytes (PBLs) from the first centrifugation were used for the extraction of germline genomic DNA. The genomic DNA of frozen tumor tissue and matched peripheral blood lymphocytes samples were isolated using a commercially available DNeasy Blood & Tissue Kit (Qiagen, Hilden, Germany). The genomic DNA of FFPE samples were isolated using Maxwell® RSC DNA FFPE Kit (Promega, Madison, WI, USA). The DNA concentration was measured using a Qubit fluorometer and the Qubit dsDNA HS (High Sensitivity) Assay Kit (Invitrogen, Carlsbad, CA, USA). The total DNA yield must be greater than or equal to 1 µg,while 260/280 and 260/230 is greater than or equal to 1.8 and 2, respectively.