Advances in Clinical Application of Cerebrospinal Fluid Circulating Tumor DNA 
in Leptomeningeal Metastasis of Non-small Cell Lung Cancer.

Leptomeningeal metastasis (LM) is a lethal complication of malignant tumors, with an incidence rate of 3%-5% among patients with non-small cell lung cancer (NSCLC). LM poses significant challenges in diagnosis, has poor prognosis, limited treatment options, and lacks standardized criteria for evaluating therapeutic efficacy, making it a difficult aspect of NSCLC management. Circulating tumor DNA (ctDNA), shed from tumor cells and carrying cancer-related information, holds significant value in precision oncology. Cerebrospinal fluid (CSF), present in the subarachnoid space of the brain, the spinal cord, and the central canal, and in direct contact with meningeal tissues, serves as the fluid medium that best reflects the genetic characteristics of LM. In recent years, CSF ctDNA has become a focal point due to its multi-omics features, playing a crucial role in the management of central nervous system (CNS) metastatic tumors. Its applications span the entire continuum of care, including aiding in diagnosis, assessing treatment response, predicting prognosis, and analyzing resistance mechanisms. This article provides a concise overview of CSF ctDNA detection techniques and their clinical applications in patients with NSCLC-LM. .