EGFR and neoplasm: This genomic plasticity facilitates clonal selection and the emergence of drug-resistant subpopulations under therapeutic stress—a process consistent with the "stress selection theory." For example, under targeted therapy, tumor cells that carry eccDNA enriched with resistance-associated genes (e.g., MET, ABCB1, or mutant EGFR alleles) may be preferentially selected, contributing to disease relapse and progression.