This reduced detection rare likely reflects several contributing factors: (i) the high diversity of exon 19 deletion subtypes with variable breakpoints, whereas our crRNA was designed against the most common subtype; (ii) technical variability in cfDNA quality and yield, influenced by plasma processing, leukocyte contamination, and freeze–thaw history; and (iii) biological heterogeneity in ctDNA shedding depending on tumor burden, metastatic site, and concurrent EGFR-TKI therapy. Here, EGFR is linked to neoplasm.