T242
Laser capture microdissection was firstly performed in biopsies to get high purity of NPC tumor cells for DNA extraction24. Genomic DNAs of tumor and paired peripheral blood samples were isolated using QIAGEN DNeasy Blood & Tissue Kit (QIAGEN, Hilden, Germany) according to the protocol. Adapter ligation and DNA cluster preparation were subjected to the Solexa sequencing. To minimize the likelihood of systematic bias in sampling, at least two paired-end libraries with insert size of 500bp were prepared for all samples and were then subjected to whole-genome sequencing, resulting in at least 30-fold haploid coverage for each sample.