More in detail, the longitudinal tracking of ctDNA, performed by NGS just before the start of targeted therapy (baseline, T0), six months later (T1), and at progression (P), showed that BRAF p.T599dup became undetectable during response and rebounded at progression both in plasma (MAF 0.33%) and in pleural effusion ctDNA (MAF 44.3%). This evidence concerns the gene BRAF and Pleural effusion.