For example, various gene promoters were found to be differentially methylated in ctDNA between patients with lung cancer and controls, including short stature homeobox 2 (SHOX2) (78, 79), doublecortin like kinase 1 (DCLK1) (80), septin9 (SEPT9) (81), ras association domain family 1 isoform A (RASSF1A), and retinoic acid receptor B2 (RARB2) (82). This evidence concerns the gene SHOX2 and lung cancer.