The prognosis of synchronous and metachronous bilateral breast cancer in Chinese patients.

This study was undertaken to determine the differences in the clinicopathology and survival between synchronous bilateral breast cancer (sBBC) and metachronous bilateral breast cancer (mBBC). Additionally, we analyzed the risk factors for single tumors to develop as sBBC or mBBC. Of the 190 bilateral breast cancer (BBC) cases, 84 cases were sBBC and 106 were mBBC. We defined sBBC as two tumors that developed within 12 months, while mBBC was defined as two tumors that developed over more than 12 months. The peak age of onset of the first mBBC tumors was significantly younger than that of sBBC tumors (p = 0.001). There was a higher concordance rate of ER/ER positivity and PR/PR positivity in the first and second tumors of sBBC than mBBC. The two sBBC breast cancers had relatively similar hormone conditions because of the low rate of ER and PR transformation from positive to negative or vice versa. We determined that patients who presented with extracapsular extension (p = 0.008) and ER positivity (p = 0.001) tend to have synchronous cancers, while patients with 3+ HER2 were more likely to develop metachronous tumors. The prognosis for mBBC was better than that for sBBC when the survival time of mBBC was measured from the initial observation of the first tumors.