Do stem-like cells play a role in drug resistance of sarcomas?

Stem cells are defined by their unique characteristics, which include their abilities to self-renew and differentiate. Normal somatic stem cells have been isolated from various tissues such as bone marrow, adipose tissue, mammary glands and the nervous system. They are considered naturally resistant to chemotherapeutic agents because they express high levels of membrane transporter molecules, detoxifying enzymes and DNA repair proteins. Several recent studies have identified the presence of side populations in various cancer tissues, the so-called 'cancer stem cells', which are defined as the counterparts of stem cells in tumor tissues. These cancer stem cells possess stem-like properties, such as self-renewal and differentiation abilities, as well as playing a role in tumor initiation. Most sarcomas, which are thought to originate from mesenchymal stem cells, are highly malignant and approximately 30-40% of them show local and/or distant relapse (metastasis), even in the case of relatively chemosensitive tumors such as osteosarcomas and Ewing sarcomas. Several studies have suggested the presence of stem-like cell populations in sarcomas, based on their tumorigenicity and drug resistance. This review explores the issues of drug resistance of cancer stem cells in sarcomas and the possibilities of targeting cancer stem cells for the future treatment of sarcomas.