The entire genome of a cancerous cell contains significantly less methylcytosine than the genome of a healthy cell. In fact, cancer cell genomes have 20-50% less methylation at individual CpG dinucleotides across the genome.[13][14][15][16] CpG islands found in promoter regions are usually protected from DNA methylation. In cancer cells CpG islands are hypomethylated [19] The regions flanking CpG islands called CpG island shores are where most DNA methylation occurs in the CpG dinucleotide context.