The primary objective is to determine whether pretreatment-to-posttreatment changes in circulating multigene methylation levels correlate with objective response rates (ORR) assessed by contrast-enhanced CT/MRI and levels of serum tumor markers. Secondary endpoints include: (a) time-dependent association between methylation fluctuation patterns and progression-free survival (PFS), (b) comparative diagnostic accuracy of methylation indices versus conventional biomarkers, and (c) feasibility of using methylation thresholds to guide adaptive therapy modification.