[en] PURPOSE: To compare the outcome of bilateral breast cancer patients to that of patients with unilateral disease. MATERIALS AND METHODS: From 1960-1995, 1254 stage O/I/II/III patients with primary breast cancer were treated by either mastectomy or breast conservation therapy at Thomas Jefferson University Hospital. There were 1141 (91.2%) unilateral, 41 (3.1%) synchronous and 65 (5.7%) metachronous breast cancer patients. Synchronous breast cancers were defined as having a second cancer diagnosis within one year of initial diagnosis. There were 46.2% of patients stage O/I at initial diagnosis, while 68% were stage O/I at subsequent diagnosis. For the metachronous breast cancers, the median interval between first and second diagnosis was 44 months (range of 13-287 months). Median follow-up time was 58 months for the synchronous cancers (15-218 months) and 107 months (21-360 months) for the metachronous cancers. Overall and NED survival, local control and distant metastatic disease rates from the time of the first and second diagnosis were calculated for the synchronous and metachronous patients. These were then compared to the unilateral breast cancer patients and to each other. RESULTS: Synchronous bilateral breast cancer patients had a worse 5 and 10 year NED survival rate (71.2% and 57.0%) compared to the unilateral patients (83.8% and 77.8%) p=.015 and also a higher distant metastasis rate (70.6% and 54.9% vs. 83.5% and 77.8%) (p=.005). Local control and overall survival comparisons were not statistically significant in this group when compared to unilateral patients. There was also no difference noted when comparing metachronous to unilateral patients for the above parameters. When analyzing metachronous and synchronous patients there was a trend revealing a worse NED survival at 5 and 10 years (84.5% and 82.2% vs. 71.2% and 57% p=.07) and a higher metastatic rate (85.9% and 80.9% vs. 70.6% and 54.9% p=.01) in the synchronous group. CONCLUSION: We conclude that bilateral breast cancer patients who present with synchronous disease are at greater risk for distant metastatis than women with unilateral breast cancers and patients with metachronous tumors. There was no difference in overall survival or local control when comparing metachronous and synchronous bilateral patients to those with unilateral disease or to each other