LAUSR

Background: Leptomeningeal metastasis (LM) is an uncommon complication in patients with solid tumors, associated with poor survival. However, LM appears to be more frequent in lung cancer patients with EGFR mutations, posing a unique clinical challenge to treating physicians. Case Presentation: We report the case of a 68-year-old Asian man with metastatic lung adenocarcinoma harboring an EGFR L858R mutation, which was initially treated with gefitinib. He developed disease progression 1 year later. Re-biopsy of the right lower lobe primary lesion revealed only an EGFR L858R mutation in the absence of a T790M mutation. The patient also experienced persistent confusion and generalized fatigue, and magnetic resonance imaging (MRI) of the brain demonstrated extensive LM. At this time, a liquid biopsy revealed an EGFR T790M mutation. Following initiation of treatment with osimertinib, the patient exhibited a rapid response with MRI of the brain showing substantial improvement of the LM after 6 months. Unfortunately, the LM recurred after 1 year at which time the patient declined further systemic chemotherapy. Conclusion: To our knowledge, this is the second reported case of LM in a patient with lung cancer harboring an EGFR T790M mutation that was successfully treated with osimertinib.