Abstract
Leptomeningeal disease (LMD) in advanced non-small cell lung cancer (NSCLC) carries a poor prognosis and is challenging to diagnose without invasive biopsy. Traditional cerebrospinal fluid (CSF) cytology considered the gold standard in diagnosis is only 33% sensitive and often requires patients to undergo multiple lumbar punctures to receive an accurate diagnosis. Innovative technologies that utilize cerebrospinal fluid (CSF) based liquid biopsy have facilitated the detection of tumor derived DNA as a surrogate for cytology, at a much earlier time period than imaging would indicate a definitive diagnosis. This study presents a 47-year-old male diagnosed with non-small cell lung cancer who presented with an increase in intraocular pressure. Subsequent testing using the Belay Summit™ test revealed an EGFR T790M mutation in the CSF. Following the detection of this variant, the patient received treatment with osimertinib (Tagrisso®), which proved beneficial for his condition.