Cancer stem cells: The root of tumor recurrence and metastases

Despite the progress in the prevention, diagnostics and treatment, cancer remains a major cause of morbidity and mortality around the world. According to the world health organization (WHO), more than 14 million newly diagnosed cases and more than 8 million deaths were reported in 2012, and increase in new cases of cancer by 70% and cancer related deaths by 45% is expected over the next 2 decades. Metastatic tumors are the cause of more than 90% of cancer related deaths due to the fact that current therapies frequently fail to provide durable curative response if tumor is spread. In this review, we summarize the main common hallmarks and evolving concept of cancer stem cells and metastasis initiating cells, their dynamic interaction with microenvironmental factors, discuss perspectives of using cancer stem cells and circulating tumor cells as prognostic and predictive tumor biomarkers as well as possible strategies for their targeting in the clinical setting.