Functional characterization of genes potentially regulated by estrogen receptor and/or ERBB2 oncogene: implications in the diagnosis, prognosis and treatment of breast cancer

Abstract

The cancer is the most commonly diagnosed neoplasm and the major source of morbidity and mortality among women worldwide. In Brazil, breast cancer is one of the most frequent malignancies in women and the leading cause of mortality. Data from the Ministry of Health estimates the occurrence of 48.930 new cases of breast cancer in 2006, representing an important health problem (INCA, Ministério da Saúde, 2006). Over the past years several studies were performed looking for the identification of genetic alterations that could be used as biomarkers in breast cancer, however, with few exceptions, such as the case of the oncogene HER/neu over expression, no validated prognostic and predictive markers do exist at present. To date, the most significant biomarker routinely used in the clinical practice is the presence of hormone receptors, estrogen and progesterone receptors, considered to be a favorable prognostic factor and an indicator of response to hormonal therapy. Hormone receptors and HER/neu over expression are both prognostic and predictive factors for breast cancer. Currently, the great deal of breast cancer research has been the identification of new diagnostic and prognostic factors for the disease and the understanding of critical signaling pathways involved in the carcinogenic process of the breast, which could provide the knowledge base for the identification of new therapeutic targets and new predictive markers of tumor sensitivity. Using different techniques for gene expression analysis, such as DDRT-¬PCR, cDNA microarray, SAGE and Real Time PCR, in primary breast tumors regarding the presence or absence of ER and PR (NAGAI et aI., 2003a; NAGAI et aI. 2004) and two human mammary luminal cell lines expressing different levels of ERBB2 before and after intensive exposure to docetaxel (DOS SANTOS et al., in press; DOS SANTOS et aI., manuscript in preparation) we identified a large number of differentially expressed genes that could be considered as potential candidate markers for breast cancer. However, the functional role or clinical significance of these genes in breast cancer development and progression is still unknown. The present study involves a group of qualified researchers with different expertise aiming to investigate the functional role and the prognostic value of the differentially expressed genes identified by our group in breast cancer. To achieve these goals six sub-projects will be performed. The first four are experimental studies involving the use of cell culture system in monolayer's and in 3D, transient transfection with expression vectors and suppression of gene expression by small interfering RNA (siRNA). In the fifth and sixth sub-projects the Tissue Microarray Technique (TMA) will be used to evaluate the clinical and prognostic significance of new candidate tumor markers in a large and well-characterized series of tumor samples and benign lesions of the breast. In addition, the expression of several panels of genes involved in different biological pathways will also be analyzed by IHC on TMAs. Principal investigators from four different institutions (Faculdade de Medicina da USP, Instituto de Ciências Biomédicas da USP, Hospital do Câncer e Escola Paulista de Medicina) and several students will participate in the present project. The expected results of the present project will likely lead to a better understanding of the molecular bases of the tumorigenic process of the breast and molecular identification and validation of new clinically important diagnostic and prognostic markers and targets for the application of novel therapeutics strategies for breast cancer patients. (AU)