On the other hand, baseline ctDNA genotyping showed that amplifications or clonal mutations of genes related to receptor tyrosine kinase (RTK)/RAS and PI3K, which comprise previously described resistance mechanisms to HER2-targeted therapy in breast cancer and gastric cancer8,9, were markedly enriched in non-responders (Fig. 2a and Supplementary Table 4). Here, ERBB2 is linked to breast cancer.