EpCAM (CD326) has diverse roles in cell adhesion and proliferation, and is known to be overexpressed in primary breast carcinomas (PBCs). While clinical and preclinical data suggest a role for EpCAM in metastases, the only prior study of EpCAM expression in breast cancer metastases suggested that EpCAM expression is decreased after first-line chemotherapy. This study evaluates EpCAM expression in metastatic breast carcinoma (MBC) versus matched PBC . Rapid autopsies were performed on 17 patients with widely metastatic breast cancer. Single patient tissue microarrays (TMAs) were constructed from archived PBC and post-mortem MBCs. In total, 169 spots from 17 PBCs and 895 spots from 195 MBCs were labeled for EpCAM by immunohistochemistry (IHC). Expression was scored as intensity (1-3) multiplied by percent membrane labeling (0-100%) and was subclassified as low (0-100), moderate (101-200), or high (201-300) labeling. PBCs exhibited exclusively low-moderate EpCAM labeling. EpCAM labeling was present in all metastases and was significantly increased in MBCs of 14 of 17 patients (P value range < 0.05 to < 0.0001, t test). In the remaining three patients, EpCAM labeling was nonsignificantly increased in 1 and unchanged in 2. High Ep- CAM labeling was verified using a different antibody for IHC, as well as in a separate series of surgically resected metastases compared to unmatched surgically resected primary breast cancers. In conclusion, EpCAM is highly expressed in MBCs compared to matched PBCs, verifying that it is a promising therapeutic target. © Springer Science+Business Media, LLC. 2009.
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