Evaluation of Trastuzumab Anti-Tumor Efficacy and its Correlation with HER-2 Status in Patient-Derived Gastric Adenocarcinoma Xenograft Models

The aim of the study was to investigate trastuzumab anti-tumor efficacy and its correlation with HER-2 status in primary xenograft models derived from Chinese patients with gastric adenocarcinoma. Patient-derived gastric adenocarcinoma xenograft (PDGAX) mouse models were firstly generated by implanting gastric adenocarcinoma tissues from patients into immune deficient mice. A high degree of histological and molecular similarity between the PDGAX mouse models and their corresponding patients’ gastric adenocarcinoma tissues was shown by pathological observation, HER-2 expression, HER-2 gene copy number, and mutation detection. Based on Hoffmann’s criteria in gastric cancer, three models (PDGAX001, PDGAX003 and PDGAX005) were defined as HER-2 positive with fluorescence in situ hybridization (FISH) amplification or immunohistochemistry (IHC) 2+/ 3+, while two models (PDGAX002, PDGAX004) were defined as HER-2 negative. Upon trastuzumab treatment, significant tumor regression (105 % TGI) was observed in model PDGAX005 (TP53 wt), while moderate sensitivity (26 % TGI) was observed in PDGAX003, and resistance was observed in PDGAX001, 002 and 004. A significant increase in HER-2 gene copy number was only observed in PDGAX005 (TP53 wt). Interestingly, trastuzumab showed no efficacy in PDGAX001 (HER2 IHC 3+ and FISH amplification, but with mutant TP53). Consistent with this finding, phosphor-HER2 modulation by trastuzumab was observed in model PDGAX005, but not in PDGAX001.