Molecular Characterization of Patient-Derived Xenograft Models

Formalin-fixed and paraffin-embedded tissue blocks of the 50 PDX models were prepared. Candidate targets, including EGFR, HER3, MET, and PD-L1, were stained via immunohistochemistry (IHC) using anti-EGFR antibody (#4267, Cell Signaling Technology, Danvers, MA, USA), anti-HER3 antibody (#2708, Cell Signaling Technology), anti-MET antibody (#790-4430, Ventana Medical Systems, Tucson, AZ, USA), and anti-PD-L1 antibody (#M4420, Spring Bioscience Corp., Pleasanton, CA, USA) according to the manufacturers’ instructions. IHC results were evaluated according to a previously published method [11 (link)–13 (link)]. Fluorescent in situ hybridization (FISH) was performed for MET and EGFR genes using the MET/CEN7 Dual Color Probe Kit (Zytovision, Bremerhafen, Germany) and EGFR/CEN7 Dual Color Probe (Zytovision) according to the manufacturer’s instructions. Gene amplifications were defined as the ratio of MET/CEN7 ≥ 2.2 and EGFR/CEN7 ≥ 2.2. All of the IHC and FISH results were reviewed and scored by two independent pathologists blinded to each other.