Activation Of Pi3k/Akt/Mtor Pathway In Er Plus Breast Cancer: Analysis Of Paired Primary And Metastatic Tumor Samples.

577 Background: The activation of the mammalian target of rapamycin (mTOR) pathway is associated with resistance to endocrine therapy in breast cancer. Our aim was to evaluate changes in activation of the PIK3/AKT/mTOR pathway between primary and corresponding metastatic tumor samples in estrogen receptor (ER) positive breast cancer patients and to test whether phosphorylated protein levels are predictive of overall survival (OS). Methods: Phosphorylated forms of AKT (p-AKT) and S6 (p-S6) were assessed by immunohistochemistry on archival paraffin embedded samples of primary breast tumors and distant metastases collected from 132 breast cancer patients in two centers. A semi-quantitative scoring system (H-score) was used, combining the intensity of staining and the percentage of stained cells. The difference between expression of p-AKT and p-S6 in primary and metastatic tumor samples was analyzed using the Wilcoxon signed-rank test and the correlation of expression of p-S6 with OS using the Cox’s proportio...