Megabase-sized hypomethylated zones in tumor cell genomes associated with fragile sites. Red and green lines represent the hypomethylated zones in MCF7 and MDA-MB-231, respectively. Blue lines represent 86 common fragile sites in human genome. We found that 79% of fragile sites were in the hypomethylated zones in the MCF-7 genome (P < 0.01), and this correlation was also significant in the MDA-MB-231 genome (P < 0.01).