CDKN2A and central nervous system cancer: ccfDNAs in glioma were associated with differential methylation levels of MGMT, cyclin-dependent kinase inhibitor 2A, multiple tumor suppressor 1 p16/(INK4a), p73, and retinoic acid receptor beta (RARb) (Balana et al., 2003; Weaver et al., 2006; Wakabayashi et al., 2009).