CDKN2A and breast carcinoma: In breast cancer patients, researchers have looked at the methylation patterns of two tumour suppressor genes, RRP22 and P16, as well as histone modifications such as methylation at lysine 4 of histone H3 (H3K4), acetylation at lysine 9 of histone H3 (H3K9), acetylation at lysine 16 of histone H4 (H4K16), and methylation at lysine 20 of histone H4 (H4K20) [20,72,157].