Prognostic and Treatment Predictive Markers Associated with Cyclin D1 Gene Amplification and Epithelial-Mesenchymal Transition in Breast Cancer

Abstract: Endocrine resistant breast cancer is a major therapeutical challenge and accurate selection of patients susceptible to certain types of anti-hormonal treatment strategies is pivotal. Discovery of novel biomarkers potentially predicting treatment response as well as the clinical course of breast cancer is essential to effectively improve therapies and diagnosis. The main goal of this thesis was to identify putative markers for prediction of clinical outcome and response to tamoxifen, the first-line endocrine treatment option for premenopausal breast cancer patients. The markers examined were associated with CCND1 amplification (Chk1 and β-arrestin1), which has previously been linked to a potential adverse effect of tamoxifen, or with epithelial-mesenchymal transition (Snail), a biological process crucial for the development of metastasis. Immunohistochemical analyses of the biomarkers were predominantly performed in a breast cancer cohort including premenopausal patients randomly assigned to receive either tamoxifen or no adjuvant treatment. The in vitro studies investigated the regulation of EMT in hypoxia, in a panel of human breast cancer cells lines. We found that deletion of the CHK1 gene is potentially associated with CCND1 amplification, and loss of Chk1 protein expression was demonstrated to be linked to an impaired response to tamoxifen in premenopausal breast cancer patients. Additionally, the EMT-regulator Snail, which has been reported to be involved in ER- signaling, was shown to predict tamoxifen response, where absence of nuclear Snail rendered patients less sensitive to this adjuvant therapy. Moreover, hypoxia induced an incomplete EMT in vitro, and Snail modulated the migratory propensity of breast cancer cells. Finally, stromal expression of β-arrestin1 was found to be an independent prognostic marker in a cohort of both pre- and postmenopausal breast cancer patients. In premenopausal patients both high expression and absence of β-arrestin1 was linked to poor prognosis, but expression of this protein was not associated with an altered tamoxifen response. In conclusion, these studies revealed two biomarkers with potential clinical significance in predicting the sensitivity to adjuvant tamoxifen, as well as one with an impact on clinical outcome.