CDKN2A and head and neck squamous cell carcinoma: Folate deficiency is associated with hypermethylation of the p16INK4A (CDKN2A) gene in human head and neck squamous cell carcinoma (HNSCC) and a rat model of hepatocellular carcinoma (Kraunz et al. 2006; Pogribny et al. 2004).