<p>Breast cancer, characterized by significant heterogeneity, remains one of the leading causes of malignant mortality in women. Chemotherapy and radiation therapy remain the most common treatments for this disease, but they are not always effective in advanced cancers due to the development of drug resistance. Therefore, the development of new therapeutic concepts and drugs, which will enable a shift toward personalized medicine, is a highly pressing task. The development of new therapeutic concepts and drugs represents a paradigm shift toward personalized medicine. The essential trace element selenium is known to possess potent anticancer properties, which have been studied and described in numerous scientific papers. Over the past two decades, particular attention has been paid to the development and research of selenium-based nanocomposites and nanocomplexes for their therapeutic anticancer properties. This review summarizes the developments and scientific advances in breast cancer therapy using selenium-containing agents of various types. This review describes recent studies on the role of inorganic and organic selenium-containing compounds, nanoselenium, and selenoproteins in breast cancer therapy. This information will not only allow us to evaluate the latest advances in selenium-based breast cancer treatment but will also help expand our understanding of the mechanisms regulating their therapeutic action.</p>