Clinical Activity of Pan-HER Inhibitors Against HER2-Mutant Lung Adenocarcinoma

HER2 mutations are found in 2% to 4% of non–small-cell lung cancer and are usually mutually exclusive with other genetic alterations. In this study, tissue specimens from 360 Korean patients were screened by direct sequencing, and 29 (8.1%) HER2 mutations were confirmed. There was a modest activity of poziotinib or afatinib, and the main toxicities were nausea, diarrhea, and mucositis. Introduction: HER2 mutations are found in 2% to 4% of non–small-cell lung cancer cases and are usually mutually exclusive with other genetic alterations. We screened a large cohort of patients from multiple institutions in Korea, described the characteristics of HER2-mutant cases, and reported on several patients who were treated with pan-HER inhibitors. Patients and Methods: The study population consisted of 360 patients diagnosed with adenocarcinoma from 4 institutions in Korea from June 2015 to September 2016. Tissue specimens from all participants were screened by direct sequencing, and next-generation sequencing was conducted only on specimens that were positive in direct sequencing. HER2-targeted therapy, either poziotinib or afatinib, was orally administrated. Results: Next-generation sequencing was conducted in 129 patients, and finally 29 (8.1%) patients with HER2 mutation were identified. Most patients were female (58.6%), had never smoked (70.0%), and had stage IV non–small-cell lung cancer (55.2%). For all patients, the histologic type was adenocarcinoma, with no coexisting EGFR or ALK alterations. The most common type of HER2 mutation (48.3%) was c.2326_2327insTGT in exon 20. A partial response was observed in 2 patients who received poziotinib and 1 patient who received afatinib. The main toxicities of the pan-HER inhibitors were nausea, diarrhea, and mucositis. Conclusion: HER2 mutation was estimated at a frequency of approximately 8.1% in Korean patients with adenocarcinoma in the absence of known driver mutations. Because some of the HER2-mutant cases responded to poziotinib or afatinib, further studies are warranted.