Analysis of CSF ctDNA from a cohort of 26 patients with leptomeningeal metastases from non-small cell lung cancer (NSCLC) revealed their unique genetic profiles, including mutations in several driver genes, copy number variations (CNVs) in MET, ERBB2, KRAS, ALK, and MYC, and loss of heterozygosity in TP53 [76]. The gene discussed is ALK; the disease is non-small cell lung carcinoma.