**2. Methods**

### *2.1. Patients and Sample Preparation*

The study enrolled 37 patients who had undergone surgery for multiple lung cancers in our department between January 2015 and July 2019. Written informed consent for genetic research was obtained from all patients, which was performed in accordance with protocols approved by the institutional review board in our hospital. Histological typing was performed according to the World Health Organisation (WHO) classification (3rd edition) [2] and clinical staging was performed according to the International Union Against Cancer Tumor-Node-Metastasis (TNM) classification (8th edition) [3].

A serial section from formalin-fixed, paraffin-embedded (FFPE) tissue was stained with hematoxylin-eosin and subsequently microdissected using an ArcturusXT laser capture microdissection system (Thermo Fisher Scientific, Tokyo, Japan). DNA was extracted using the QIAamp DNA FFPE Tissue Kit (Qiagen, Tokyo, Japan). FFPE DNA quality was verified using primers for the ribonuclease P locus. Peripheral blood was drawn from each patient immediately before surgery. A buffy coat was isolated by centrifugation and DNA was extracted from these cells using the QIAamp DNA Blood Mini Kit (Qiagen).
