We treated 18 patients with advanced HER2-mutant lung adenocarcinomas...The partial response rate was 44% (95% CI, 22% to 69%), meeting the primary end point...Responses were seen in patients with HER2 exon 20 insertions and point mutations in the kinase, transmembrane, and extracellular domains...Concurrent HER2 amplification was observed in two patients. HER2 immunohistochemistry ranged from 0 to 2+ and did not predict response, and responders had low HER2 protein expression measured by mass spectrometry...The median progression-free survival was 5 months (95% CI, 3 to 9 months).

In this report, a 67-year-old male patient was diagnosed with advanced lung adenocarcinoma...The results of genetic testing indicated a non-frameshift insertion mutation in exon 20 of the ERBB2 gene. The patients received T-DM1...Partial response appeared in the tumor lesions after treatment for four cycles, and PET-computer tomography showed the tumor lesions were effectively controlled, and the efficacy evaluation was complete response after treatment for six cycles.