The first genome-wide DNA methylation study was presented by Rapado-González et al. [61], who identified a group of novel DNA methylation markers specific for tongue cancer in the saliva of OSCC patients: A2BP1 (Fox-1 homolog A, also known as ataxin 2-binding protein 1), ANK1 (ankyrin 1), ALDH1A2 (aldehyde dehydrogenase 1 family, member A2), GFRA1 (GDNF family receptor alpha-1), TTYH1 (tweety family member 1), and PDE4B (cAMP-specific 3′,5′-cyclic phosphodiesterase 4B). This evidence concerns the gene ALDH1A2 and tongue cancer.