“…In this study, a clear discordance was found between primary tumor and DTCs. The acquisition of HER2 amplification in DTCs, while the primary tumor is negative, can be explained with a selective advantage conferred by HER2 to DTCs during dissemination [21,25,47,48,49,50], or with a higher tendency of the HER2-positive DTC clones to detach from the primary tumor and to spread [25,48,49,50,51,52]. We found that 23.6% of patients presented a HER2-negative primary tumor and HER2-positive DTCs.…”