We therefore chose to evaluate the expression status of DNMT1 and HDAC1 as the most important epigenetic enzymes involving DNA methylation and histone modification accompanied with expression changes of ERα. Gene expression status at the protein and mRNA levels in both xenograft and spontaneous breast tumors were detected by western-blot assays and real-time PCR. The gene discussed is DNMT1; the disease is breast neoplasm.