Abstract P6-04-27: EBAG9 immunoreactivity is a potential prognostic factor for poor outcome of breast cancer patients with adjuvant tamoxifen therapy

Abstract

Abstract Estrogen receptor-binding fragment associated gene 9 (EBAG9) is a primary estrogen responsive gene originally cloned from MCF-7 human breast carcinoma cells. Upregulation of EBAG9 expression has been observed in several malignant tumors such as advanced breast cancers, indicating that EBAG9 may contribute to tumor progression. In the present study, the immunohistochemical analyses of EBAG9 were performed using the specimens from breast cancer patients treated with tamoxifen as adjuvant therapy. To investigate the association between EBAG9 expression and the therapeutic effect of tamoxifen in breast cancer, we used adjuvant tamoxifen-treated breast cancer patient tissues from 3 institutions. The study was approved by the institutional review board. Patients with distant metastases within 5 years after surgery followed by tamoxifen treatment were defined as relapse cases, whereas those without distant metastases were defined as relapse-free cases. The immunoreactivity of EBAG9 was predominantly detected in the cytoplasm of breast cancer cells. Notably, EBAG9 immunoreactivity level was substantially elevated in the breast cancer samples from the relapse patients, and the positive immunoreactivity of EBAG9 was correlated with poor prognosis of the patients with adjuvant therapy. These results suggest that EBAG9 expression in tumor regions is associated with unfavorable prognosis of patients with adjuvant tamoxifen therapy and EBAG9 immunoreactivity can serve as a biomarker for adjuvant tamoxifen efficacy. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-04-27.