PURPOSE: c-myc and HER2 have been reported be amplified in 20% to 30% of clinical breast cancers and appears to be related with poor clinical outcome. The relationship between amplification of c-myc and HER2 and other clinical and biological characteristics of the breast cancers, including clinical outcome, are described. METHODS: c-myc and HER2 amplification were analyzed on 225 consecutive non-selected breast cancers by fluorescence in situ hybridization using tissue microarray technology. RESULTS: c-myc was amplified in 33 cases (15.4%) and HER2 was amplified in 49 cases (23.3%). c-myc amplification was significantly increased with HER2 amplification (p<0.001) and closely linked with cell proliferative activity measured by Ki67 labeling index (p=0.010). In univariate survival analysis, lymph node status, tumor size, and histologic grade of the tumors were significant prognostic factors. However, lymph node status was the only significant prognostic factor for predicting patient survival in multivariate analysis. Patient survival was not different according to c-myc amplification status and c-myc amplification showed no significant correlation with clinco-pathologic parameters of the tumors. CONCLUSION: A strong correlation between c-myc and HER2 amplifications, and cell proliferative activity indicate a biologic link between c-myc and HER2 in breast cancer.