What is the role of nanotechnology in diagnosis and treatment of metastatic breast cancer? Promising scenarios for the near future

Metastatic breast cancer represents a diagnostic and therapeutic challenge due to tumor heterogeneity and to various physiological barriers that hinder drug delivery to the metastatic sites. To overcome these limitations, nanoformulated drugs have been developed and tested in preclinical studies, and few of them have been successfully translated into clinical practice. In particular, liposomal anthracyclines and nanoformulated albumin-bound paclitaxel have revealed an improved therapeutic index when compared to conventional chemotherapy, with significant reduction of drugs toxicity. Several strategies for nanoparticles engineering have more recently been explored to increase selectivity for tumor cells and to reach poorly accessible metastatic districts. Targeted nanoparticles, directed toward tumor markers and tissue-specific metastases, may provide effective devices in case of lowvascularized and small-sized metastases, thus paving the way for a real change in the natural history of metastatic disease. A number of targets have been identified and exploited for surface functionalization of different types of nanoparticles, which are currently undergoing preclinical studies. The aim of this review is to provide an overview of current nanotechnology applied to metastatic breast cancer diagnosis and treatment. Promising results encourage an upcoming translation of this research into clinical practice for an effective management of the disease in the near future.