C-myc and HER2 amplification were analyzed on 214 consecutive breast cancers by fluorescence in situ hybridization using tissue microarray technology. The frequencies of amplification were 15.4% (33/214) and 23.3% (49/210), respectively. c- myc amplification was significantly associated with HER2 amplification ( P < .001) and closely linked with cell proliferative activity, measured by Ki67 labeling index ( P = .010). In univariate survival analysis, lymph node status, tumor size, and histological grade were significant prognostic factors, but in multivariate analysis, lymph node status was the only significant factor. Patient survival did not differ according to c- myc amplification status, and c- myc amplification showed no significant correlation with clinicopathologic features of the tumors. A strong correlation between c- myc and HER2 amplification and proliferative activity indicates a biological link between these genes in breast cancer cell.