Identification of differentially expressed microRNAs in human male breast cancer

The expression of 319 microRNAs was analyzed in 9 primary human male breast tumors and in epithelial cells from 15 male gynecomastia specimens using fluorescence-labeled bead technology. For identification of differentially expressed microRNAs data were analyzed by cluster analysis and selected statistical methods.Expression levels were validated for the most up- or down-regulated microRNAs in this training cohort using real-time PCR methodology as well as in an independent test cohort comprising 12 cases of human male breast cancer.Unsupervised cluster analysis separated very well male breast cancer samples and control specimens according to their microRNA expression pattern indicating cancer-specific alterations of microRNA expression in human male breast cancer. miR-21, miR519d, miR-183, miR-197, and miR-493-5p were identified as most prominently up-regulated, miR-145 and miR-497 as most prominently down-regulated in male breast cancer.Male breast cancer displays several differentially expressed microRNAs. Not all of them are shared with breast cancer biopsies from female patients indicating male breast cancer specific alterations of microRNA expression.Breast cancer in men accounts for approx. 1% of all breast cancers [1]. Despite a statistically significant raise in the incidence of male breast cancer over the last 25 years it is still a quite rare disease. Therefore, therapy is mainly based on what is known from female breast cancer. Despite the fact that randomized controlled prospective trials are not possible due to the low incidence, it is clear from retrospective analyses that male breast cancer is not exactly the same entity as female breast cancer [2].The discovery of a new class of small non-protein-coding RNAs with pleiotropic regulatory functions ("microRNAs") has substantially changed our understanding of tumor development and progression [3]. New molecular mechanisms, new diagnostic markers and new potential therapeutic targets have been discovered