[Lung Adenocarcinoma with EGFR Exon 20 H773_V774delinsLM Mutation 
Sensitive to Furmonertinib: A Case Report].

Epidermal growth factor receptor (EGFR) exon 20 mutations represent a rare subset of genetic alterations in non-small cell lung cancer (NSCLC). Among them, the complex mutation H773_V774delinsLM is exceedingly uncommon, accounting for only 0.2%-1% of all EGFR mutations. It is currently believed that rare EGFR mutations are generally resistant to the first- and second-generation EGFR-tyrosine kinase inhibitors (EGFR-TKIs). Although the third-generation EGFR-TKIs have shown some efficacy in certain rare mutations, clinical evidence regarding their use in NSCLC patients with the H773_V774delinsLM mutation remains sparse, and their efficacy and safety are yet to be clarified. Here, we present the first documented case of a patient with EGFR H773_V774delinsLM-mutant lung adenocarcinoma who experienced remarkable tumor regression following treatment with furmonertinib. This case highlights the potential utility of furmonertinib in treating patients with this rare EGFR mutation and may provide valuable insight into emerging treatment strategies for similarly affected patients.
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