Amplification of the human epidermal growth factor receptor 2 ( HER2 ) gene is associated with a microsatellite stable status in Chinese gastric cancer patients

Background Gastric cancer (GC) is one of the most common cancers worldwide. However, little is known about the combination of HER2 amplification and microsatellite instability (MSI) status in GC. This study aimed to analyze the correlation of HER2 amplification with microsatellite instability (MSI) status, clinical characteristics, and the tumor mutational burden (TMB) of patients. Methods A total of 192 gastric cancer (GC) patients were enrolled in this cohort. To analyze genomic alterations (GAs), deep sequencing was performed on 450 target cancer genes. TMB was measured by an in-house algorithm. MSI status was inferred based on the MANTIS (Microsatellite Analysis for Normal-Tumor InStability) score. Results The most frequently amplified genes in the GC patients included cyclin E1 (CCNE1), human epidermal growth factor receptor 2 (HER2), fibroblast growth factor receptor 2 (FGFR2), cyclin D1 (CCND1), fibroblast growth factor 19 (FGF19), fibroblast growth factor 3 (FGF3), and fibroblast growth factor 4 (FGF4). The frequency of HER2 amplification was 9.38% (18/192). HER2 amplification was higher in females than in males (14.52% vs. 6.92%, respectively, P=0.091), however, MSI was higher in males compared to females (7.69% vs. 4.84%, respectively, P=0.46). HER2 amplification was higher in metastatic loci compared to primary lesions (23.08% vs. 8.38%, respectively, P=0.079) and was lower in patients with high TMB (TMB-H) compared to those with low TMB (TMB-L) (4.0% vs. 11.35%, respectively, P=0.12). While the frequency of MSI in metastatic foci was higher than that in primary lesions (15.38% vs. 6.15%, respectively, P=0.48), MSI status was highly associated with TMB-H (20% vs. 0%, respectively, P=3.66×10-7). Furthermore, HER2 amplification was negatively correlated with MSI status in Chinese GC patients. Conclusions HER2 amplification was negatively correlated with TMB-H and MSI status, and MSI status was significantly associated with TMB-H in Chinese GC patients. These data suggested that HER2 amplification might be a negative indicator for GC immunotherapy.