DLL4 and breast cancer: Since the promoter region of DLL4 contains a typical CpG island (Figure 4A), we examined the methylation state in genomic DNA isolated from eight cell lines (five LFS cell lines, one breast cancer cell line (MCF7), one neuroblastoma cell line (IMR32), and normal human foreskin fibroblast cell line HS27), utilizing methylation-specific PCR (Figure 4B).