Durable response to osimertinib in EGFR mutated T790M wildtype non-small cell lung cancer with leptomeningeal metastases: A case report.

In patients with non-small cell lung cancer (NSCLC) progression with leptomeningeal (LM) metastases is a catastrophic event with limited treatment options. We report a patient who developed leptomeningeal disease while on front-line erlotinib. High-dose tyrosine kinase inhibitor was started but ineffective. She was transitioned to third-generation TKI osimertinib, despite lacking a T790M mutation, and responded with complete resolution of symptoms and malignant cytology in the cerebrospinal fluid (CSF). Recent phase one data and our case indicate osimertinib should be viewed as a best practice for treatment of LM disease in epidermal growth factor receptor (EGFR) mutated NSCLC regardless of T790M status.