Abstract A120: Dissecting the role of AGR2 in breast cancer

Breast cancer is the most common women′s malignity, with growing incidence primarily in advanced countries. Hormone sensitive tumors, characterized by expression of estrogen and progesterone receptors, represent the largest group of breast carcinomas. The presence of estrogen receptors (ER) and progesterone receptors (PgR) indicates response to endocrine therapy and improved disease-free survival (1). The most frequent therapy for estrogen receptor positive breast cancer malignancies is functional blockage of estrogen receptors by tamoxifen. Although tamoxifen is treatment of choice and estrogen receptor targeting is responsible for improvements in cure rates of breast cancers, the therapy itself is limited by frequently developed drug resistance (2). As the endocrine resistance is a significant problem in breast cancer treatment, identification and validation of novel resistance determinants is important to improve treatment efficacy and patient outcome. In our previous work we have found that AGR2 expression is elevated rather than inhibited in response to tamoxifen, thus we have evaluated the function of AGR2 during anti-hormone therapy. Our in vitro results clearly showed that AGR2 promotes viability of cells exposed to tamoxifen. Consequently AGR2 activation through the ER was confirmed by chromatin immunoprecipitation and reporter assays (3). To reveal if AGR2 expression correlates with patient outcome or just mirrors hormonal levels in particular patients, we have determined the AGR2 expression in Tru-Cut needle biopsies from tamoxifen treated postmenopausal breast cancer patients. We found that AGR2 mRNA levels are inversely associated with primary treatment response (p=0.0011) and progression free survival (p=0.0366) indicating that elevated AGR2 expression predicts decreased efficacy of tamoxifen treatment. From this perspective, AGR2 is a potential predictive biomarker enabling selection of an optimal algorithm for adjuvant hormonal therapy in postmenopausal ER-positive breast cancer patients. What is interesting, AGR2 expression could be less frequently detected also in estrogen receptor negative breast carcinomas. Analysis of consecutive group of breast tumors revealed that except estrogen receptor positive cases, AGR2 expression is associated with the HER2 molecular subtype especially, indicating that HER2 overexpression may influence AGR2 levels. These data are consistent with our recently published work showing involvement of PDPK1-AKT sign