EGFR and neoplasm: Monitoring the allele frequency of these variants in circulating tumor DNA (ctDNA) during therapy enables early detection of resistance-associated mutations (e.g., EGFR T790M), prompting timely switching to next-generation inhibitors [43,44], such as the well-recognized false-negative ctDNA results in low-shedding tumors (e.g., early-stage prostate or pancreatic cancers), which can obscure emerging resistance [45].