HER2 exon 20 insertion mutations in lung adenocarcinoma with leptomeningeal metastasis: a case report and response to poziotinib

Leptomeningeal metastasis (LM) is associated with poor prognosis and represents a terminal event of non-small cell lung cancers (NSCLC). In previous studies, most of LM-patients have detected epidermal growth factor receptor (EGFR) mutation and responded to the third generation of EGFR-tyrosine kinase inhibitor (TKI). This study aimed to report a case of ERBB2 (HER2) exon 20 insertion mutations in the cerebrospinal fluid (CSF) of LM-patient which response to poziotinib. At the beginning, postoperative pathology showed a primary invasive adenocarcinoma with no mutations in EGFR and ROS-1. Pemetrexed plus carboplatin combined with bevacizumab was administered as the first-line followed by bevacizumab alone for continuation maintenance therapy. Targeted therapy and immunotherapy were given after the disease progressed in two months. Subsequently, the patient developed mental symptoms and adenocarcinoma cells were found in the CSF. Next-generation sequencing (NGS) results showed HER2 exon 20 insertion mutations in the primary tissue, CSF and plasma samples. Then, poziotinib was administered and the symptoms improved significantly after 3 days and the progress free survival was nearly 2 months. Therefore, we speculate that the CSF concentration and penetration rate of poziotinib may significantly higher than of other TKIs so that it achieves a higher CSF concentration than standard dosing, and successfully controlled LM. It may provide a new therapeutic option for LM-patient and may be especially who are lung adenocarcinoma with HER2 exon 20 insertion.