ABSTRACT
<p><b>OBJECTIVE</b>To investigate the different expressions of ER and ER gene status between primary and relapsed/metastatic lesions and their clinical significance.</p><p><b>METHODS</b>ER and ER gene status of primary and relapse/metastatic breast cancer masked in 70 metastatic breast cancer patients were assessed by determination of methylation status by immunohistochemistry (IHC) and methylation specific polymerase chain reaction (MSP), respectively.</p><p><b>RESULTS</b>Positive rate of ER in the primary breast cancers was 64.3%, and in the relapse/metastatic lesions was 41.4% (P < 0.05). There were six patients whose positive ER status was changed to negative, among them the ER gene status was changed from demethylation to hypermethylation in four cases. Another four patients with negative ER status changed to positive, and their ER gene hypermethylation changed to ER demethylation status.</p><p><b>CONCLUSIONS</b>The discordance of ER expression status in primary and relapse/metastatic lesions of breast cancer might be related to DNA methylation status.</p>