Patient-Derived Xenograft (PDX) Mouse Models

PDX models were established from tumor specimens collected under an approved institutional review board protocol and have been arbitrarily designated DF, DY, DC, and EK to ensure no patient information is shared. Briefly, tumors were minced, mixed with Matrigel, and implanted subcutaneously in 6- to 8-wk-old female NSG mice (Jackson Laboratories). Once established, tumors were maintained and expanded by serial subcutaneous transplantation. All patient samples had gastric human epidermal growth factor receptor 2 (HER2)–positive tumors. DF and DY were from the same patient at different stages of disease. Tumor samples were evaluated by immunohistochemistry and graded for HER2 and MET expression, with DC, DF, DY, and EK all being graded 3+ for HER2 expression (high), and 3+, 1–2+, 2+, and 3+ for MET, respectively. HGF levels in these tumors were not evaluated before this study.