This prespecified biomarker analysis was performed on longitudinal samples collected from two phase II clinical trials (NCT02535507: n = 15, NCT02834936: n = 60) which evaluated the efficacy and safety of pyrotinib in HER2-mutant advanced lung adenocarcinoma after platinum-based chemotherapy (Fig. 1a). Here, ERBB2 is linked to lung adenocarcinoma.