Proteomics-based characterization of potential biomarkers in tamoxifen resistance in breast cancer.

628 Background: Despite the success of tamoxifen (tam) since its introduction there are patients with an estrogen (ER) and progesterone receptor-positive breast cancer (BC) that do not benefit from therapy. This represents a significant clinical problem acknowledging the need for reliable and useful predictive biomarkers. Techniques such as mass spectrometry (MS) enable simultaneous analyses of multiple proteins opening up possibilities in which to study the involvement of various pathways in the resistance mechanism. Our aim is to identify novel potential biomarkers predicting the effect of tam. Methods: Out of a consecutive patient cohort of primary ER positive BC stage I-II, subjected to adjuvant tam, 12 patients with early relapses within 2 years of tam treatment and 12 responsive (relapse-free > 7 years) were selected. MS was used to investigate proteomic changes between groups. Tumor homogenates were subjected to bottom up proteomics suggesting that quantification and identification occurred after s...