Genomic DNA was extracted from the tumor tissues of patients with lung adenocarcinoma using the QIAamp Fast DNA Tissue Kit (Qiagen, Valencia, CA, USA) according to the manufacturer’s instructions. Exons 18–21 of the EGFR gene were amplified using the polymerase chain reaction (PCR) and were then subjected to the DNA sequencing reaction using the ABI PRISM 3130XL System (Applied Biosystems, Foster City, CA, USA) as described previously [28 (link)].
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