Cancer stem cells: lessons learned from the leukemic stem cells

Cancer is the second cause of death in Turkey and the frequency of cancer deaths increased from 12% in 2002 to 21% in 2009 (Ozkan et al., 2013). To win the war on cancer, we certainly need to apply well-planned prevention policies, given that it is caused mostly by environmental factors, and to develop more effective therapies. To achieve a cure for the disease, it is crucial to understand the cellular and molecular mechanisms leading to cancer and to therapeutically target all the factors playing a role in the initiation, progression, maintenance, and relapse of the disease, preferably in the form of personalized therapy. One of the biggest challenges faced during the diagnosis and treatment of tumors, especially those arising from tissues composed of heterogeneous cell populations such as hematopoietic tissues, is to find the cell of origin or the cancer-initiating cell. Knowing the cell of origin can help in dissecting the normal features of the target cell from its abnormal cancerous form; moreover, this knowledge provides insight into the early events leading to a malignant transformation and eventually shapes the treatment protocols. Initial and ongoing studies in leukemia elegantly showed how to identify the cell of origin (or the stem cells of cancers) and how to calculate their frequency and evolution during disease progression. This minireview summarizes the current view on cancer stem cells, and particularly leukemic stem cells, and their potential role in the initiation, maintenance, and therapy resistance of cancer.