CDKN2A and gastric cancer: In some, such as lymphoma, gastric cancer, head and neck squamous cell carcinoma (HNSC), liver and oesophageal cancers [18–22], p16INK4A/CDKN2A downregulation is caused by promoter hypermethylation, but it can also be due to histone deacetylase (HDAC) activity [23].