Downregulation of EGFR in a metastatic brain lesion of EGFR-mutated non-small cell lung cancer using a tyrosine kinase inhibitor: A case report

Brain metastasis is a common complication in patients with cancer, with lung cancer being the most frequent origin of brain metastases. Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) have begun to serve a pivotal role in lung cancer treatment and have been reported to demonstrate anticancer activity against brain metastases by penetrating the blood-brain barrier. The present study reports, to the best of our knowledge, the first case of EGFR-mutated non-small cell lung cancer (NSCLC) brain metastasis that was surgically resected while the lesion was responding to the EGFR-TKI erlotinib. The results of the present study demonstrated that EGFR-mutated NSCLC cells were able to evade the cytotoxic effect of EGFR-TKI by downregulating EGFR expression, without exhibiting the T790M EGFR mutation.